PHP Domain Parser v2: Tracks v2 changes

IDNA support and the required extensions should have triggered a major version change.  This is the PR for the new major version.

The `isSuffixValid` functionality is thanks to @SmellyFish and would have been added in #36 had it not required some bug fixing (my bugs, not @SmellyFish's) and some refactoring.  Big thanks to @SmellyFish for the original PR.