Docs: decrease depth of index from 4 to 2.

This hides the subpackage of the test suite and its tests, which we don't
really care about much.  It'll also leave just links to sub-sections (and not
sub-sub-sub-sections) of user guide docs that are forthcoming.
Docs: Add a basic user guide.

I can't check all of these or push to PyPI (for the installation instructions)
because our wifi network is being all wonky (again).  Sometimes I just don't
want to do network troubleshooting after spending all day doing server
troubleshooting. -_-
Docs: add quick-look section to index page.

Starting off with an index is boring and uninteresting.  Requests does it
beautifully[0]: a small amount of text saying what it is, and a short little
example showing off how awesome it is.  PyFixit isn't as awesome as requests,
but it'd be nice if the docs were as good.

[0]: http://requests.readthedocs.org/en/latest/