Refactored: PathFilter into dedicated class.
Updated: Docs for PathFilter.
Refactored: Moved creation of PathFilter out of FilteringDiffIterator.
Refactored: Moved creation of PathFilter up in the creation chain.
Refactored: Moved creation of PathFilter up in the creation chain.
Refactored: Finished moving up the creation of PathFilter.
Fixed: Behat tests after recent refactorings.