Oops, forgot to add QuantHash, moritz++
Add nqp::p6invokehandler.

Hides away a Parrot specific detail. Cleans up one place in Actions,
but the debugger is the main beneficiary.
Change .elems to .total for Sets/Bags, .elems is now what you expect for a hash
Move set operators to their own file, for clarity and ease of maintenance
Slight optimization in Str / pick / roll
[...]**0..1 to [...]? for dec_number

Also strip call to filter_number().
Normalize Baggy.gist to make consistent with future Mixy.gist
Initial implementation of Mixy / Mix / MixHash, as per spec (almost)
implement List.combinations(Range $)