Point at 2.7
Less repetitive repetetive.
Remove py33 from tox.
Reorder toxenvs.
Load meta-schemas via pkgutil rather than searching the filesystem.

Hopefully this makes things like cx_Freeze work, but they appear to all be
special snowflakes and this doesn't appear easy to test.

Credit to @pjdelport for helping clear away some of the smoke.

Closes #161, #162