Release v0.17.0

Added Scope.is_top to determine if the scope is the top-level scope (outside of any binds)
Add an optional emit_bind_edges parameter to all save_dot graphviz functions which you can use to omit the dashed lines connecting bind nodes to nodes allocated in their scope
Expose For_analyzer module in the Incremental interface for traversal of Incr nodes for analysis purposes.

Release v0.16.0

Add incr_memoize library for memoizing incremental binds. This library keeps the incremental nodes of old binds alive by storing them in a data structure.
- Introduce Store_params submodule for configuring the memoization behavior.

Adds a Let_syntax module to Incremental_intf.S. We've found things like this useful in a couple of different projects as a nice alternative to the mapN functions.

Made it possible to use Incremental without invalidation -- i.e. a change in a the left-hand side of bind does not invalidate nodes created on the right-hand side.

This is configurable via the argument to Incremental.Make_with_config, which now takes:
```
val bind_lhs_change_should_invalidate_rhs : bool
```
So, one can now build an Incremental without invalidation using:
```
Incremental.Make_with_config (struct
  include Incremental.Config.Default ()
  let bind_lhs_change_should_invalidate_rhs = false
end) ()
```
Implementation

The implementation is simple: When a bind rhs changes, instead of invalidate_nodes_created_on_rhs, we rescope_nodes_created_on_rhs, which moves the nodes up to the bind's parent.

Testing

Turned the unit tests into a functor parameterized on bind_lhs_change_should_invalidate_rhs, and run them with both true and false. Modified tests where necessary to skip tests of invalidity when bind_lhs_change_should_invalidate_rhs = false.

Added a unit test of bind_lhs_change_should_invalidate_rhs = true that makes sure a node created on a bind rhs whose lhs subsequently changes continues to stabilize correctly.
Splitted incremental into a part that can run in javascript, incremental_kernel, and the other one.

Add README.org to Incremental.
Added some type annotations based on comments by @def-lkb about lack of principality.
Switched to ppx.