BUG : fix for text path rendering issues

Suggested by @leejjoon.

Fixes #2889
symlog-scale: Remove asssert linscale >= 1.

I can't see why the assert was needed and it does excatly what i would expect from it.
Don't store cache lookups in the file.  Invalid the cache when font
family parameters change.
Don't explicitly rebuild font cache in test.
Modest performance improvement.
Minor fix to commit 24bc071

Still pep8 compliant.
Merge pull request #3080 from khyox/master

Minor fix to commit 24bc071
Updated tests, and added a new test for PathEffectsRenderer points_to_pixels.
Merge pull request #3081 from pelson/points_to_pixels

Points to pixels
DOC : Added CHANGELOG entry
Merge branch 'font-manager-state'
Merge branch 'patch-1' of git://github.com/Tillsten/matplotlib into Tillsten-patch-1

Conflicts:
	CHANGELOG
Merge branch 'Tillsten-patch-1'