Merge pull request #3004 from mdboom/docs-nxutils

FAQ and unit/ still refers to nxutils
Merge pull request #3246 from dmcdougall/fix-doc-links

Fix some hyperlinks in the documentation

Edits only in rst files
DOC : change how OO/pyplot/pylab is addressed

I assume this will be controversial

Addresses #3115
DOC : grammer fixes and doc edits

 - removed from pylab import *
 - changed some wording
DOC : edits to usage_faq.rst
Merge pull request #3243 from pelson/nbagg_proper

Fixed backend workflow.
Merge pull request #3217 from JulianCienfuegos/master

Added some function arguments to the documentation for FuncAnimation
Two
moves libpng from optional to required
TST: Fix test_backend_ps failures on Windows
TST: do not remove files while they are open

Fixes WindowsError: [Error 32] The process cannot access the file because it is being used by another process
BUG: do not remove file if passed in file object

Fix WindowsError: [Error 32] The process cannot access the file because it is being used by another process
TST: On Windows open files can not be removed
TST: fix test errors on Python 3
Add animation.convert_path setting to matplotlibrc.template
Stop make.py removing generated documentation figs
Merge pull request #3249 from cgohlke/patch-1

TST: Fix test_backend_ps failures on Windows
STY: remove unused imports in plot_directive
STY: pep8 2 lines between functions

pep8 for plot directive.
MNT: remove Python 2.7 copy of relpath

Matplotlib now depends on Python 2.6, which has relpath