make some continuations smaller by not storing the index
make some continuations smaller by not storing the index

this hides the index in the ast. there is some fixed cost to that by
making the stored program bigger, but shouldn't be very bad. it saves
one word per continuation, and removes the check of the index when
reducing the continuation.

vishesh/pycket,samth/pycket,vishesh/pycket,samth/pycket,vishesh/pycket,pycket/pycket,pycket/pycket,magnusmorton/pycket,cderici/pycket,cderici/pycket,magnusmorton/pycket,krono/pycket,magnusmorton/pycket,pycket/pycket,cderici/pycket,krono/pycket,samth/pycket,krono/pycket