Add tests for fix_range

Currently failing due to lib2to3.fixes.fix_range being used.
Turn off lib2to3.fixes.fix_xrange

Allows fix_range to do all the work (although it’s still failing its
new tests).
Get fix_range working

Had to simplify the pattern in the fixer as I just couldn’t get it to
work with a single argument while also working with 2 or 3 arguments.
Add tests mixing range() and xrange()
Merge pull request #51 from brettcannon/fix_range

Make fix_range work for both range() and xrange()