- Implement TIB, #TIB (characters read), and >IN (relative
  address of last character read in TIB).
- Use absolute instead of relative address for positions
  of Forth variables.
- Use HERE for word buffer instead of Forth variable.
- ".S" prints a lot of zeros that don't exist on the stack. Fix
  this.
- Write documentation in NROFF.
- Prefix "wd_" to all function names used as Forth built-in word.
- Add support for the Block words.
- The word S" leaves nothing on the stack. Fix this.
- Write a front end for 80286 bare metal with Turtle graphics using Mode X.
- Write some more simple Forth programs for testing the virtual machine.
- Write a front end that extends the built-in words to support Turtle
  graphics.
- Write a text adventure game that works in this Forth, PForth, and GForth.
