Forth-based unit tests

[eigenhombre]

• ensure TRUE (signed -1) and FALSE (0) can be represented properly in current implementation
• add = word (consume top two items; place TRUE if they are equal, else place FALSE on stack
• add ASSERT word which does something like: : assert ( flag -- ) 0= if ." Assertion failed!" abort then ; (eventually, do this without hard-coding)
• add ability to interpret a file
• have test.c or another program interpret a file with assertions