[grt-talk] Pattern API changes

[Nikodemus Siivola]

Of the exported symbols those used to generata pattern functions begin with
MAKE-, while hardcoded pattern functions are called by the name of the
pattern (CHECKER, GRADIENT). Also, I replaced MAKE-CHECKER by CHECKER,
since that should cover 99% of the usage -- and being prepared for the 1%
eventuality just ain't worth the additional FUNCALL.

I think that this is getting good enough for 0.1, but still not the final
solution: I think that has to be integated with object and pigment
constructors (and normal constructors as well, once we have them).

Cheers,

  -- Nikodemus