Trailing whitespaces removal
Documentation fixes: cleanup in OAuth2StorageLaravel inline doc (some elements where refering to original PDO class) and typos corrections
Error message mismatch fix
Added namespace declarations in interfaces to allow smooth inheritance if developer extends OAuth2StorageLaravel to handle other grant types.
Removed leading backslashes in namespace declarations to conform to PHP guidelines.
Replaced 'echo' by 'die' at the end of OAuth2::grantAccessToken().
IT MAY BREAK BACKWARD COMPATIBILITY if people did something in their controller after calling the function. However, it's more consistent with the other output functions (e.g. Oauth2::finishClientAuthorization) and as the library handles the entire response (headers and body) it allows to keep its process internal.
Otherwise if user does not use a die() or exit() explicitely in its controller, Laravel will for example overwrite the 'Content-Type' header from 'application/json' to 'text/html'.
Really no reason to hardcode a maximal limit for client_id length
Added a placeholder method for exception handling, as the class calls it but the method itself had missing