Make AccessToken serializable
[AccessToken] Add isExpired function
Merge pull request #154 from yguedidi/better-access-token

AccessToken additions
Added ext-mbstring to composer require.
Merge pull request #161 from SammyK/mbstring-in-composer

Added ext-mbstring to composer require.
Adding developer site doc content, needs lots of updates.
Add FacebookApp entity
Namespace tests and add licence header
Merge pull request #163 from yguedidi/namespace-tests

Namespace tests
Merge pull request #162 from yguedidi/facebook-app-entity

Add FacebookApp entity
Rename FacebookRequestException to FacebookResponseException
Add serialization test and test copyright header to FacebookApp entity
Add FacebookRequest entity
Add FacebookResponse entity
Add FacebookBatchRequest entity
Add FacebookBatchResponse entity
Add FacebookClient class
Update FacebookResponseException to use FacebookResponse
Add Code entity
Update AccessToken entity and associate it with a FacebookApp entity