Travis now provides Python 3.4
Added pytest-cache to tox.ini

This allows you to only run the last failed tests using `py.test --lf`
or `tox -- --lf`.
Implemented support for namedtuples (fixes #107)

Note that namedtuples are only supported for Python >2.6.
Merge remote-tracking branch 'origin/namedtuple' into dev
Merge remote-tracking branch 'origin/travis_py34' into dev