Word routines

This is the description of all word routine you can encounter
in this Forth implementation. That is, a wordref will always
point to a memory offset containing one of these numbers.

0x17: nativeWord. This words PFA contains native binary code
and is jumped to directly.

0x0e: compiledWord. This word's PFA contains an atom list and
its execution is described in "EXECUTION MODEL" above.

0x0b: cellWord. This word is usually followed by a 2-byte value
in its PFA.  Upon execution, the *address* of the PFA is pushed
to PS.
                                                        (cont.)
