Enhance coding style & structure

* CS fix regarding to PSR1&2 (https://github.com/fabpot/PHP-CS-Fixer)
* One class per file
* Fixes some namespace issues
* Remove some obsolete checks (class exists on 5.0/5.1 classes, pecl dependencies, ...)

BC breaks :
* All NewsFeedParser* classes have been moved into their own namespace : for example ``Opensearchserver\NewsFeedParser_Atom_Entry`` has been renamed into ``Opensearchserver\NewsFeedParser\Atom\Entry``
* Same change for OssIndexDocument* classes : for example ``Opensearchserver\OssIndexDocument_Field `` --> ``Opensearchserver\OssIndexDocument\Field``