Add a MIME type for SRT files

Fix a bug that would throw a type error in `GraphEdge` in some cases

Add check for PHP 7 CSPRNG first to keep mcrypt deprecation messages …

…from appearing in PHP 7.1 (facebookarchive#692)

Fix a bug that does not properly parse response headers when they con…

…tain the colon character

- Bump Graph API version to v2.8.

- Auto-cast `cover` field to `GraphCoverPhoto` and `picture` field to `GraphPicture` in `GraphPage`. (facebookarchive#655)
- Add `getCover()` and `getPicture()` to `GraphPage`. (facebookarchive#655)

Fix bug where polyfills file fails to included properly when using th…

…e built-in auto loader

Bump Graph API version to v2.7

- Fix notice that is raised in `FacebookUrlDetectionHandler` (faceboo…

…karchive#626)

- Fix bug in `FacebookRedirectLoginHelper::getLoginUrl()` where the CSRF token gets overwritten in certain scenarios (facebookarchive#613)
- Fix bug with polyfills not getting loaded when installing the Facebook PHP SDK the manual way (facebookarchive#599)

Bump Graph version to v2.6; add new Birthday class; add better error …

…checking for app IDs

Remove mbstring extension dependency