fast_fish

Create a faster than normal fish with specified performance (and thus corresponding precision tradeoff), values tolerance can hold: NULL and "default", means do same as fish, other values understood in increasing order of speed gain are: "exact" "precise" "fast" "glitch"

Fast fishes should be cached, since they are not internally kept track of/made into singletons by babl and many creations of fast fishes will otherwise be a leak.