Merge pull request #16 from dssg/docs

basic documentation

**Changes**

* rounded out library docstrings, such that the heart of the (API) documentation is there
* integrated with Sphinx (and autodoc)
  * such that standard documentation can be generated from docstrings, (tho HTML currently unused)
  * submitted patches to extension [sphinx-contrib.restbuilder](sphinx-contrib/restbuilder#8), such that Sphinx can also build RST docs – (it's a little surprising that Sphinx can't on its own or otherwise its build process can't be intercepted to retrieve RST formatted output before it's parsed into an abstract tree, considering its input is RST, albeit Sphinx- and autodoc-extended RST; but, nonetheless, this appeared to be the easiest way forward ... though markdown is another obvious target, it doesn't cleanly support all the directives that you get from RST ... and Github won't render README.html).
  * scripted a development command to generate HTML docs and README.rst

In the end, I don't love [how the auto-generated README.rst looks](https://github.com/dssg/ohio/tree/docs), at least not as Github renders it; but, for something like this, I think it's fine, and keeps API documentation in the code.

A discussion of [benchmarking the Pandas extension](#11) is included in `doc/index.rst` (and from there included in built documentation).

resolves #1

.gitignore

@@ -64,7 +64,7 @@ instance/
 .scrapy
 
 # Sphinx documentation
-docs/_build/
+doc/_build/
 
 # PyBuilder
 target/