Merge pull request #62 from mgrandi/mgrandi_master

Documentation improvements and fixes to user provided format_validators
0.9.2
fix bad commit
0.9.3 fix
small changes to usage.rst, to make it so a horizontal scroll bar doesn't appear in the 'custom formatter' section
made a string formatting call consistant with the python2 way of doing it instead of python3
small change in comments