Make symbols for keywords beforehand.

Before:
> lua lualisp.lua < ../zslisp/car_rec.zsl  2.00s user 0.02s system 97% cpu 2.065 total
After:
> lua lualisp.lua < ../zslisp/car_rec.zsl  1.87s user 0.02s system 95% cpu 1.980 total
Add simple loop syntax.