BUG/API : relax validation in hist

Relax the validation on input data to hist.

 - up-convert scalar to length 1 list
 - don't error out for length 1 input data

closes #3882
MNT : slight refactor of Axis.set_ticklabels

update both labels (top/bottom or left/right), even if
they are not both visible.
Fallback to free fonts in text
Fallback to Bitsream vera sans mono

In logo example
Install humor sans when building docs
Add Felipa to cursive fonts
Install Felipa on Travis
Simplfy set_boxstyle Accepts section

Change it to something that can actually be passed by docscrape and displayed in the setp docs
Merge pull request #3942 from tacaswell/axis_refactor

MNT : slight refactor of Axis.set_ticklabels
Correct Accepts string
TST : added test of relaxed validation in hist
Merge pull request #3954 from jenshnielsen/accepts_issue

DOC : Simplify set_boxstyle Accepts section of FancyBboxPatch
Merge pull request #3883 from tacaswell/hist_validation_relax

BUG/API : relax validation in hist
Merge pull request #3950 from jenshnielsen/travis_text_fixes

DOC/TST : Ensure that fonts are present on travis when building docs.
API : tighten validation on pivot in Quiver

only accept {'mid', 'middle', 'tip', 'tail'} instead of
being super permissive.

Closes #3951
PEP8 : comment-related pep8

Fixes 'violations' we don't test for, all white space in comments.