Update sidebar.
added new links to sidebar
Converted API_CHANGES to reST and included it in the documentation tree.
New custom colormap example; and fix typo in Axes.autoscale_view
Improved docstrings in colors.py
Use autoscale_view for contour plot autoscaling
Fixed all Gtk memory leaks exercised by D2Hitman's recent thread.
Further memory leak fixes for Gtk
Reduce memory leakage in Gtk+-based backends. Still far from perfect.
Turn off mixed-mode rendering when svg.image_noscale is True.
