Fix #1999: dash value of zero causes infinite loop
Merge pull request #1999 from mdboom/dashes-infinite-loop

Setting dashes to (0,0) results in infinite loop for agg backends
Fix #2006: stretch is invalid, introduced in cc61700
Allow Paths to be marked as readonly, mark all of the singletons as readonly, and deepcopy those Paths in tests that need to modify the path.
fix #2005: Animated artists should be included when saving to a file
Add docstrings
Use with statement for assert_raises
Fixes a number of bugs introduced by cc61700.  texmanager will now still pass when font.family is a list of strings (though there's no sane way for LaTeX to deal with that, but that's nothing new).
Merge pull request #2006 from mdboom/fix-stretch-invalid

ValueError: stretch is invalid
Make weighting by position in the list less magical
Long line
Merge pull request #2003 from pelson/hatch_clipping_v1.2.x

Fixed hatch clipping.
Don't use 'with assert_raises', it doesn't work on Python 2.6
Fix #2015: After the baseline refactoring in #1810, baseline handling was broken for text.usetex = True.  This brings it inline with everything else (where the assumption is that y == 0 is the baseline and not the bottom).
Merge pull request #2010 from mdboom/immutable-paths

Allow Paths to be marked as readonly
Merge remote-tracking branch 'upstream/v1.2.x' into HEAD

Conflicts:
	src/_backend_agg.cpp
Update baseline images
Merge pull request #2012 from mdboom/texmanager-family-list

texmanager doesn't handle list of names for `font.family`
Merge pull request #2015 from mdboom/usetex-baseline-fixes

Wrong text baseline with usetex.
Fix #2016: reading memory past the end of a C++ std::vector