Updating to work with GuzzleHttp 5.0

- updating composer.json to allow for both 4.0 and 5.0
- removed fluent interface usage in OAuth1
- updating OAuth1Test to work with 5.0. Moved the `GuzzleHttp\Adapter\Transaction` to `GuzzleHttp\Transaction`. *note:* this is bc incompatible with 4.0

Signed-off-by: RJ Garcia <rj@bighead.net>
Merge pull request #21 from ragboyjr/master

Fix to work guzzlehttp 5.0
Implement OAuth2 subscriber

This is mainly an import of `kamermans/guzzle4-oauth2-subscriber` repository,
which is an adaptation of `commerceguys/guzzle-oauth2-plugin` for Guzzle4,
plus some additionnal customisations.
Refactored token persistence and other improvements

This is squash of commits:

- 4c2d44b Refactored token persistence, added support for GitHub Application OAuth, allowed manually setting access_token
- 35125f0 Removed inheritdoc comments
- ae078cd Updated class comment
- ddf9531 Adding unit tests
- 2aaab9f Added TokenFactory tests  - [x] Add some tests
- 4a04d04 Added Signer tests
- 6c28fdb Refactored to use Guzzle-style testing namespace
- 7b44036 Added grant type test
- db3155d Fixed typos, added more unit test
- 521b7c3 Added persistence tests
- 5c8c1f9 Switched to the Guzzle History subscriber for mock request testing to avoid nasty anonymous scope inspection
- 0c37011 Update composer.json
Split token factory from serialization
Fix coding style

- Remove blank lines between <?php and namespace
- Make service attributes private
- Remove author tags
- Fix docblocks
- Fix spaces on string concatenation
Update to guzzle5