Make AccessToken serializable
[AccessToken] Add isExpired function
Added ext-mbstring to composer require.
Adding developer site doc content, needs lots of updates.
Namespace tests and add licence header
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
Add DebugAccessToken entity
Update SignedRequest entity and associate it with a FacebookApp entity
Update helpers to use FacebookClient and FacebookApp
Add request and batch request builders