Consider switching documentation from custom Markdown to Sphinx + ReST

Consider moving documentation (http://libcloud.apache.org/docs/) to Sphinx.

Reasons:

• It's more idomatic / in Python world Sphinx is the standard
• We can also host it on readthedocs which is turning out to become a defacto standard for hosting docs for Python libraries

Downsides:

• Currently docs are constitent with other website content and use Markdown. For Sphinx we would need to use ReST.