Fix issues with install_data missing from the sdist package.

Added a tox.ini to allow tox to run tests in virtualenv

Add .gitignore to ignore the .tox directory created by tox and the .idea directory created by pycharm.
Expand test cases to output a diff on assertEqual failing instead of the strings which are hard to understand.
Add missing png requirement
Fix tests to not fail if run from the parent directory

Add missing PyPNG dependency
Start adding sphinx documentation
Merge pull request #22 from dwighthubbard/master

Ridiculously delayed pull merge.  Various packaging changes and bug fixes for dwighthubbard's