Feature/more str format

’Ello ‘ello!

**I’ve contined converting the old-style `%` formatting to the modern `str.format()` style.**

**However:** Since PyVows doesn’t have great test coverage for itself, **I’m requesting a human-review**. Just to make sure I didn’t break something that slipped by the tests.

Of course, I checked over my work as best I could.  But PyVows passes around objects in many clever ways that I don’t fully understand, so I can only be as confident as the current test suite allows.