matplotlib Code

Use regular expressions to do dedenting. This is ~15X faster than the
old implementation. dedent accounted for around 30% of the time spent
in "import pylab", so was probably worthy of optimization, even if this
regex approach is less clear. The results are identical to the old
implementation, with the exception of a single docstring (in
backend_bases.py) that needed to be fixed.

Fix bug where some the images of some math expressions were truncated
at the edges when using Agg backend.

Better fontconfig pattern standards compliance. Added experimental
(may be removed) fontconfig support.

Allow markup kwarg in more places.

Better mathtext error messages. Fix bug when using \sqrt without
explicit root.

Cleaned up some comments.

mathtext.* font rcParams now use fontconfig patterns to specify fonts.
Support converting FontProperties objects to/from fontconfig patterns.

Added step plot based on patch by Manuel Metz

Support get_image_magnification in pdf backend

There's no need to link ttconv with CXX (it hasn't used it for
sometime, but I forgot to remove it from the build.)