Added PhpdocSeparationFixer

Replaces #845.
If it search for something - like for next non-whitespacy token - it does return null, couse lack of that element is not an error.

If it get something that doesn't exists - eg get cache for unknown key - it throws exception.

What is the key here? It looks for something or get something from collection at given index, and if one use invalid index it should blow up ?