Ability to increment and decrement in database cache storage

Fulfilling https://github.com/laravel/framework/issues/4409
This is not atomic. The idea is that you just let MySQL know that it should do `foo = foo + 1` and you do that in the MySQL, not in PHP. If you pull an answer, plus one, then put it back things get pretty slow.

I know you've locked the row but that just seems like its asking for trouble, and all systems support `foo = foo + 1` so doing that just makes more sense, and is less code anyway.