Prettify Selection Only

I had a few funky problems with Django template tags, so I thought I would help in making a selection-only alternative to the prettify script.  Working for me.  Interested to know if there are any backwards compatibility issues.

resolves victorporof/Sublime-HTMLPrettify#67
Selection goes back to end selection
Merge branch 'patch-2' of git://github.com/bozdoz/Sublime-HTMLPrettify into bozdoz-patch-2
Merge branch 'bozdoz-patch-2'
When the selection is invalid, only message about that specific error
Rename a few identifiers for consistency and don't attempt to reselect text after formatting anymore