Move existing tests into "unit" directory
integration test for FollowRedirects

initial simple test for the purpose of discussing how we might
want to go about writing integration tests
lower required test coverage threshold

see discussion in:

  https://github.com/lostisland/faraday_middleware/pull/98
constrain simple_oauth version

https://github.com/lostisland/faraday_middleware/pull/98#issuecomment-58705269
Merge pull request #98 from jjb/integration-tests

Integration tests