Py3k and Py2k cross compat

This pull-request introduces the six package to make TempoDB cross compatible between python 2.x and python 3.x.

All tests for python 2.x pass; very few pass for python 3.x due to dictionary ordering when JSON encoding. The assertion tests test for string equality and if the dicts aren't in the same order (they are never guaranteed to be because it's an unordered data type) the tests will fail.