Python 3 compatibility fixes

Added ability to easily turn off element labels

Adding flexibility to grid plot

trying to fix travis

Tweaked tests

Moved examples, improved grid plot flexibility

Removed actual plotting part from tests

Merge branch 'master' of https://github.com/skirklin/periodic-table-plotter

Set matplotlib backend to Agg for tests

Adding build status badge to README

PyYAML to requirements

added nose to requirements

adding unittests

added requirements.txt

Added .travis.yml