Expose cursor methods for setting a selection based on a point (an object
with x and y  properties).  Points are based on the page's coordinate
system.
 - Note that innerWidth/innerHeight is used instead of width/height to
   include points in the padding
 - childForPoint also returns itself if none of its children match the
   point

Also expose clearSelection to allow the cursor’s selection to be cleared
programmatically.

Mistakenly committed childForPoint with the wrong call for each child
in the tree; rectifying by making sure that each child of a node that
contains a point calls chidForPoint so we can get the lowest node in
the tree that contains the point.

Update ReadMe to include public methods for setting and clearing
selection on static math.

This change makes it easier to select the contents inside of
delimiters. When seeking where to put the cursor for a selection, the
cursor will be placed inside the delimiters if the seek location is on
the delimiter. If the cursor is to the left of the left delimiter or
the right of the right delimiter, then the whole of the delimiter
command will be selected.

This does not affect keyboard-based selection.

Adds functionality to the API for editable fields within static math
fields (inner math fields) to make them static or editable.
makeStatic() changes the class of the editable field to
“mq-editable-field-static”, removes its texture, and unbinds its event
handlers. makeEditable() does the opposite. It wraps the functions for
initializing an editable field in an easy-to-reference way.

This approach maintains the existing tree structure and any references
to the inner editable field in the static math wrapper’s inner fields
array. This approach assumes that a static math field will take over
the event handling for an editable field after it has been made static.

This commit adds another configuration parameter for the spaceBehavesLikeTab
option.  Previously, the only valid values were 'true' and 'false'.  Where
'false' simply inserted spaces and 'true' made spaces behave like tab.  It is
now possible to add a string 'exceptRootBlock'.  'exceptRootBlock' behaves
the same as 'true' unless the cursor is in the root block, where it will
insert a space instead.

This feature allows the entry of mixed fractions in the root block, which
'true' was unable to do.

This feature is purposfully overloading the semantics of 'spaceBehavesLikeTab'
to add a new configuration option because this causes the smallest divergeance
from the MathQuill root project.  All things being equal, however, the better
change would be to rename the configuration option to 'spaceBehavior' and use
strings for all options: 'default', 'asSpaces', 'asTabs', and
'asTabsExceptForRootBlock'.  Where 'default' and 'asSpaces' are currently the
same.

By default, MathQuill allows the browser to handle Tab in the standard way
when the cursor is in the root block.  This means that the user will move to
the next focusable element in tab order.  This behavior bypasses any templates
between the current cursor position and the end.

If templates are thought of as editable areas, like mini-textfields, this
approach feels unexpected to keyboard users, who would expect 'focus' to
traverse to the next 'field,' i.e. next template.

This commit adds a new configuration property: tabAction.  By default tabAction
simply uses the current behavior.  Users can specify a value of
'escapeAndTemplate' to allow Tabs from the root block to find the next template
or to move outside of the MathQuill field if no templates exist.

Adjusting selections in a mathematically meaningful way around unary
and binary operators. Expands selections to include sibling nodes
around operators based on a few heuristics about what constitutes a
meaningful expression with basic arithmetic operators. "Meaningful
selection" is enabled with the strictOperatorSelection config flag,
which can be used with both static and editable math. The static math
API was changed to allow for config options.

Instead of specifying a default set of prefix and binary operators to
use in strict operator selection, use the prefix and binary operator
arrays passed in from the config. This changes the config option from a
simple boolean (strictOperatorSelection: true) to an object with
properties containing arrays of the control sequences we want to treat
differently during selection:

strictOperatorSelection: {
   prefixOperators: [‘-‘, ‘\\pm ‘],
   binaryOperators: [‘+’, ‘=‘]
}

The bower version that this project uses is the base version of the release,
the MathQuill release number in package.json, plus a revision number.  Our
revision number is continually increasing, such that 0.9.4-5 -> 0.10.1-6 in
the next release.  This allows us to track the main revision of MathQuill
while also keeping track of our additional features that have not been
accepted via pull request.

We should never submit a pull request to MathQuill for bower.json.

When updating to the 0.10 release, I misresolved a conflict that led me to put
the setSelection method next to the clearSelection method.  While this seemed
correct at the time, it was not.  The problem with keeping the methods in
EditableMath is that you cannot use them to create mouse selections in
StaticMath.  The select method, which is cursor-related cannot be used in
the StaticMath fields and therefore was not moved.

Updated the documentation to reflect the change in the movement of the API
methods.

Adds functionality to the API for editable fields within static math
fields (inner math fields) to make them static or editable.
makeStatic() changes the class of the editable field to
“mq-editable-field-static”, removes its texture, and unbinds its event
handlers. makeEditable() does the opposite. It wraps the functions for
initializing an editable field in an easy-to-reference way.

This approach maintains the existing tree structure and any references
to the inner editable field in the static math wrapper’s inner fields
array. This approach assumes that a static math field will take over
the event handling for an editable field after it has been made static.

…for strictOperatorSelection.

…first element in a style block.

When a binary operator was the first block inside a style block (textcolor or class), the unary/binary check failed to determine the proper state because it did not check the block to the left of the style block.  This fix recursively walks ancestor style blocks until none remain, then performs the original check.  Added new unit tests to confirm this functionality.

This is simply another Style command with custom CSS to make curved border.

This is simply another Style command with custom CSS to make a line with an
arrowhead at each end.

There were a couple of small issues here:
1. :after is used to fill empty blocks, but I need :after for the right
   arrowhead.

   This was resolved by using min-width and min-height.  Both are extremely
   common CSS at this point.

2. The original \overleftarrow and \overrightarrow work upon which this is
   based do not scale well.

   I made no effort to fix the scaling issue.  The current arrows misalign with
   the line if the font-size changes even slightly.  Using \overleftarrow in
   the visual test page, where the base font is .8em causes issues.

   Without using JavaScript to alter inline styles, I think that end users will
   have to write custom styles if they are using non-standard font sizes.  This
   is no worse than the original implementation, so I feel confident that the
   \overleftrightarrow is as good as what currently exists for the other arrow
   types.

3. The collapsed arrowheads for \overleftrightarrow collapse on top of one
   another when the block is empty.  It looks like an asterisk.

   The min-width could be made larger.  This is part of a set of geometric
   markers that need at least two identifiers underneath.  No line segment,
   ray, or line can be defined without at least two points.

   Given that the current \over* markers do not have enough space when empty
   for two characters, I concluded that two space was not necessary here
   either.  The difference, however, is that the single-arrowhead lines do not
   present a visual miscue when collapsed to a single character width.

   This would be an easy change.  Given the variable width nature of Symbola, I
   recommend that the min-width be set to 1.5em if this change is desired.
   Our custom CSS that we apply on top of MathQuill's base CSS for our product
   does use the 1.5em min-width.

…d.js.

Conflicts:
- .gitignore
     accepted master
- src/commands/math/commands.js
    kept simultaneous add
    used master order for isStyleBlock