Queryset-ify the client some more

I believe introducing the pythonic, queryset-ish interface was a good idea but I'm very unhappy with the .get() vs. .get(singular=True) situation. I would much rather have the queryset-ish interface of .get() and .filter() which would be a breaking change (the reason I originally decided against it).

Maybe utilizing git tags and/or deprecation warnings can help easing the transition.