Transform all grid lines for a given coordinate in one go, and avoid recomoputing frame patch every time a grid line is drawn.
Added entry to CHANGES.md
Removed unused code
Merge pull request #100 from astrofrog/optimize-grid-transformations

Transform all grid lines for a given coordinate in one go
added option for excluding overlapping tick labels
renamed set_exclude_overlapping method
updated docstring for exclude_overlapping
added image test for exclude overlapping
added exclude overlap to minor ticks test
putting import rc_context in try/except block
putting rcparams inside try/catch statements as well
adding pillow to travis.yml
trying using PIL instead of pillow instead
trying to use pip install for pillow
trying to backport rc_context
had accidentally changed grid alpha to 1.0
forgot to add rc_utils
adding grid.alpha key to rc_context from rc_utils
minor changes to clean up, increased tolerance to 1.5
updating changes.md