matplotlib Code

Add translucent legend example from John Hunter's mailing list example.

Fix the alignment issues with the PS backend.

No need to import mathtex in the Qt4 backend.

Port parts of the PS backend over. Alignment still needs to be checked.

Also remove the wx mathtex example on account of also belonging in mathtex.

Remove a mathtex demo from matplotlib. These now live in mathtex as opposed to matplotlib.

Port over the Cairo backend to mathtex. Just PS and OS X left.

fixed Axes.step docstring per sf bug 2823304

Port the SVG backend over to mathtex.

Fix support for hatches without color fills to pdf and svg backends.
Add an example of that to hatch_demo.py.