Added plex.py

Added Plex input plugin. Uses a Plex media server tv-section as input.
PEP8
Nicer looking urlopen
Enable sphinx doctest extension and fix rendering of TDD docs page
Include test data in tarballs
Added developer database documentation to Sphinx.
Merge pull request #48 from floppym/master

Include test data in tarballs
Merge pull request #47 from planeturban/plex

Plex
Readthedocs fixes.
Merge branch 'master' of https://github.com/Flexget/Flexget
Merge branch 'master' of https://github.com/Flexget/Flexget into discover_refactor