I have also removed default extensions to be easier to read.
Extensions that are used but enabled by default in PHP could maybe be
listed in an advanced documentation instead.
https://github.com/marienfressinaud/FreshRSS/issues/575
* Requis : [PDO_MySQL](http://php.net/pdo-mysql) ou [PDO_SQLite](http://php.net/pdo-sqlite), [cURL](http://php.net/curl), [GMP](http://php.net/gmp) (seulement pour accès API sur platformes <64bits)