Issue 1521: Cubic interpolation for triangular grids
Fixes problem raised in #1431
MEP10 - refactored hlines and vlines documentation
Modified hline and vline examples to have only one file and linked them to the documentation
DOC mentions kwargs in vlines and hlines
DOC didn't render properly
Fix Python 3 bug in PS backend.
Another Python3 bytes/unicode fix
Flush file handles at the end, since Python 3 won't do it for us.
Re-write stacked step histogram
Fix bug in stacked bar histogram. Also, calling hist with `log=True` now
behaves correctly in all cases.
Update a few test baseline images
PEP8 fixes
Remove duplicate test_hist_offset
Added 2 image tests and a non-image test. Miscellanous spelling corrections.
Merge pull request #1779 from mdboom/ps/python3

Bug in postscript backend in Python 3
MEP10 - documentation improvements on set_xlabel and text of axes.py
Merge pull request #1790 from pelson/set_transform_on_artist

Fixes problem raised in #1431 (```get_transform``` should not affect ```is_transform_set```)
Merge pull request #1724 from neggert/hist_stack_round2

Re-write stacked step histogram
improve snapping in agg backend