The following words allow you to assemble z80 binaries. Being
Forth words, opcode assembly is a bit different than with a
typical assembler. For example, what would traditionally be
"ld a, b" would become "A B LDrr,".

The "argtype" suffix after each mnemonic is needed because the
assembler doesn't auto-detect the op's form based on arguments.
It has to be explicitly specified. "r" is for 8-bit registers,
"d" for 16-bit ones, "i" for immediate, "c" is for conditions.
Be aware that "SP" and "AF" refer to the same value: some 16-
bit ops can affect SP, others, AF. If you use the wrong argu-
ment on the wrong op, you will affect the wrong register.

Mnemonics having only a single form, such as PUSH and POP,
don't have argtype suffixes.
                                                        (cont.)