[WIP] Support multiple @find-by annotations

Still open tasks but basic support for multiple ```@find-by```. Still requiring some new unit tests and ```ElementCollection``` see #48 for more details.

Closes #13
Double check argument names to match ones, that are in the interface. For example an `$offset` should in fact be `$index` (see http://php.net/manual/en/arrayobject.offsetexists.php). I bet similar naming issues are with other changed/added code.

I recommend renaming parameter via `Change Signature` refactoring of PhpStorm. This way PHPDoc won't be scrambled as it usually happens when a method parameter is directly renamed via `Shift+F6`.