Improved build matrix.

Cleaner versions syntax.
Added Django 1.7 RTM.
Added peewee 2.3.x and 2.4.x.
Used travis_retry in order to avoid build failures due to network issues.
Matrix should fast finish since it's quite large.
Excluded pony 0.5.4 since it is not supported.
Added Pony 0.6rc2 to the build matrix.
Fixed syntax.
That's probably the right one.
Excluded testing Python 3.2 with Pony ORM since it's not supported by Pony.
Fixed syntax error.
Merge branch 'patch-1' of https://github.com/thedrow/architect into thedrow-patch-1
return previous version semantics