Backport recent changes in trunk to the mathtex branch.
New version of Gouraud quadmesh shader with 4 triangles per quad.
Typo in navigation_toolbar.rst.
do case insensitive color string matching, as suggested in sf bug 2834598
update the contributing faq
add OffsetBox.contains method
add some links
more examples on how to use the extensions
a few fixes from proofreading
proper attribution
