DOC improves documentation on the pyplot module and the bar method
backend_pgf: clip paths within the backend (fixes #1857)
added rcParam for x and y margin

Addresses issue #1766
updated docs + changelog
Fixed handling of ArrowStyle class input to set_arrowstyle function. Fixes #1812
Normalize all 'e.g.' instances. Addresses issue #1423.
tweaked formatting/text in whats_new
fixing minor formatting errors introduce by the last fix of formatting
errors.
Merge pull request #1908 from tacaswell/margins_rcParam

added rcParam for x and y margin
Reformatted two longs line in artists.rst.
Added test for passing an arrowstyle class to the FancyArrowPatch (previously not working)
Updated modified lines to ensure linewidth <= 79 according to PEP8.
Merge pull request #1916 from cimarronm/normalize_eg

Normalize all 'e.g.' instances. Addresses issue #1423.
Merge pull request #1913 from cimarronm/settingarrowstylefix

Fix for issue #1812 - support for passing arrow style class instances to FancyArrorwPatch.
Merge pull request #1858 from pwuertz/pgf_path_clip

backend_pgf: clip paths within the backend (fixes #1857)
Merge pull request #1757 from NelleV/MEP10

DOC improves documentation on the pyplot module and the bar method
JRE: Fixed an error where a local variable was used before it was set.
Tidied up some of the documentation.
Updated some of the examples.
Actions by @NelleV.