Make RFC to include `standard-fish’

[spdegabrielle]

And standard-cat.

And unify pict with 2htdp/image

(And all the cool big-bang stuff, as well as the awesome spinoffs )

[mflatt]

The pict library for Rhombus is in some ways a unification of pict and 2htdp/image, in that it takes some better ideas from the latter while building on the former. The Rhombus pict library also directly supports animation and has a better story for updating a pict by replacing its part. It does not, as yet, includes standard_fish, though. Maybe it belongs in a pict/fish library. (FWIW, I think it should be implemented fresh, instead of using the old standard-fish function, which was written before gradient brushes became available.)