Add ability to use libpng-config to get linker flags
copy FontProperty objects to solve bug #3327
test for issue #3327
BUG : don't assign color to flier props if None

Close #3336
AGG link changed. Also fix other doc warnings
Add lines_api.rst and patches_api.rst
Add text_api.rst
BUG : guard marker from sym parsing in bxp

add a guard against `None` returned as `marker`
by `_process_plot_format(sym)`.
Added image and offsetbox apis to the API list.
Merge pull request #3342 from WeatherGod/14xDocFixes

DOC : fixed links, un-nested artist API docs

AGG link changed. Also fix other doc warnings
TST : added test for bxp

Adds test for case where `sym` kwarg to `bxp` does not
specify color
Merge pull request #3337 from tacaswell/bxp_flier_colors

BUG : don't assign color or marker to flier props if None
DOC: comprehensive rewrite of OSX install docs

Katy's recent edits were a big improvement, but the faq install
instructions for OSX had also got horribly out of date.  The main thing
that has changed is that wheels are now the default binary installation
format, and, even if we are going to provide eggs, no-one should be
using easy_install now.
DOC: extend instructions for Python.org Python

Also - point to 'getting help' section in troubleshooting.
DOC: fixes suggested by Thomas

Remove debugging pip for Python.org Python.

De-escalate problem heading.
DOC: fix cruft from bad edit of windows section

Thanks to Eric F for pointing it out.
DOC: fix once -> one typo; link on system python

Fix typo pointed out by Eric F; add link to wiki page on system Python
and Extras/lib.
DOC: make clear role of OSX version in dmg name

OSX version in dmg name in fact refers to Python.org Python
compatibility - but not the version of OSX it was 'built for'.
DOC: suggest xcode then help instead of vice versa

From suggestion of Eric F.
Add documentation to Travis builds.