Why is it bad to put init_words at the end of init_prims, instead of
calling init_words in main?  Does this still cause an error now that
we've robustified pc and other things?

Write FORGET.

Make colon handle "recursive" definitions all right.
As in, ": foo foo ... ;"

Variable length names.

Implement strings.
   - Strings will live in the dictionary, too.
     There will be a function, string_handler or something.  It takes
     the address of a string (starts with a count byte/word, then the
     string itself, null-terminated for friendliness to C functions.
     Must decide on byte vs. word.  Well, word is right for regular
     strings, but byte might be nice for the entry names... though
     word could do too there.)  Anyway, what this function does is
     push the address and length of the string on the stack.  Other
     primitives are used for displaying, outputting, whatever.  Hey,
     the function must increment the PC past the string and to the
     word right before the next PFA.  Need to write a macro which
     takes care of alignment automatically...

Implement variables.
   - Variables will live in the dictionary.  They get a word, whose
     name is the name of the variable.  The CFA points to
     variable_handler(), a function which pushes the next PFA on the
     stack when run (that is, the address of the PF).  It does this
     simply by pushing (PC + 1).  After that, you use standard ! and @
     operations to work with the variable.

Implement arrays.
   - Better brush up on Brodie before doing this.