0.5.0

This is a draft of the rauth 0.5.0 release, incorporating support for Requests v1.x.

Much of the rauth API and implementation has been rethought. Of particular interest is the new `session.py` module. With 0.5.0 all service wrappers will make sure of a specialized `Session` object. These objects manage the signing interpolation. They replace the previous hook infrastructure(OAuth1) and ad hoc signing(OAuth2, Ofly). 

The primary modules in need of attention for review are:

1. service.py
2. session.py
3. test_service.py (for correctness and completeness)
4. test_session.py
5. all example applications
6. CHANGELOG (for completeness)

The documentation could also use review for typos and correctness. Most of this is generated from the docstrings so typos and the like can probably be noted during review of the modules themselves.

This pull has been rebased off master to remove the unnecessary doc inclusions which were deleted in the release development process.