Improve API and general software documentation for M2C

[JTFouquier]

I made a small document containing available API endpoints & examples, but it's just a google sheet. Consider using a better method for documentation.

http://swagger.io/
https://apiblueprint.org/
http://www.mashery.com/api/io-docs

I can likely do this at a later time. Just not urgent now...

[x0xMaximus]

Django REST framework 3.4 just made some big improvements on documentation features, when doing this issue, make sure to reference the improvements and what they provide in the new release

[x0xMaximus]

How important is it to have API documentation when we're moving in the direction of having a dedicated download page for users and researchers to access? Do we want to promote people accessing our submission endpoints (I'd suggest not) or our pubtator BioC endpoints?

I foresee the public release of the /download page superseding positioning the project to become a live API resource for people to use.

Worth emphasizing that this API documentation is different than general project documentation and installation notes. I am in full support of having those, but I do not feel as though it's valuable to have our private APIs be explicitly detailed out for the public to browse when we want to direct them to a designated download page