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
Merge pull request #85 from anizami/ticks-overlap

Added exclude_overlapping option in set_ticks to prevent ticks from overlapping