Fix pythonxy link
Update index.html page.

This allows for multiple versions of the matplotlib documentation to
be made available.  The scheme is that the root
documentation (i.e. http://matplotlib.sf.net/) will always be the
latest stable version.  Other versions of the documentation will be
available in subdirectories off of the root (the latest stable version
is merely a symlink or redirect back to the root).  This is the same
convention used by "docs.python.org", as an aside.

The index.html page uses some JavaScript to load a little snippet of
HTML from "/versions.html" that lists the available versions.
"versions.html" is not part of this repository, but is part of the
matplotlib.github.com repository and is updated by hand whenever new
versions are added or removed from the archive.  This approach allows
all versions of the documentation to point to all other versions of
the documentation.  This JavaScript XMLHttpRequest magic doesn't
happen when the user is viewing static files on their local machine,
and this is a happy coincidence.

The perhaps controversial outcome of this change is that the summary
list of plotting commands is removed from the front page.  For one, we
want to steer people toward the version of the documentation that
corresponds to the version they are running.  Also, this was a
manually created list, and has become quite out of date over time.
Better, IMHO, to link to the pyplot documentation.

This freed up room to move much of the content that existed in the
sidebar to the main body, where I feel it's much less buried.  I plan
to add a lot more external resources and links, so having the room to
do this would be very helpful.

Adds a "Fork me on Github" banner.
Gentler donation language.
Update credits page
Add an autogenerated plotting command summary.
Fix small typo listing members to exclude
Add docstring to _setup_plot_info_docstrings
Update credits
Merge pull request #1067 from mdboom/doc_multi_version

Support multi-version documentation on the website
Remove hard-coded docstring on plotting()
Add a link to matplotlib questions on stackoverflow.
Add banner about John Hunter Memorial Fund.
Fix John Hunter banner
Fix PDF href