Py3k v4

This is a port of the latest Pelican 3.1.1.

**Note:** Some external libraries must also be updated for Python 3.x compatibility; see [README-PY3K](https://github.com/dmdm/pelican/blob/py3k-v4/README-PY3K.rst) for details.

Issues:
- Travis cannot yet test for Python 3.2 because py3k versions of external libs are needed
- Py26 is broken. Creation of "locale_date" uses method "encode()" with [arguments](https://github.com/getpelican/pelican/pull/618/files#L27R57) that did not exist in Python 2.6.