matplotlib Code

Removed unused imports.

Renamed [xmin, ymin, xmax, ymax] in Bbox to [x0, y0, x1, y1] and
provide functions that really do give xmax etc. as well.
Renamed lbrt to extents and lbwh to bounds (for consistency).
Removed some dead code.

figlegends work now. (Phew!) Rendering quality fixes drawing
axis-aligned line segments in Agg.

Continued progress getting more examples to work. Working examples
(with TkAgg backend only) are marked in PASSED_DEMOS for the curious.

Simplified sharing axes again.
Plowing through -- making more examples work.
First pass at updating collections (LineCollection mostly works)

Progress on agg_buffer_to_array example.

Creating branch to work on transforms/projections refactoring.