This allows us to save a whole 500 bytes on the final binary size!
This change comes after I took a look at the hex dump and saw that one letter
constants in z80a.fs took a lot of space.
Forth-ification of Collapse OS goes forward. What will happen is that assembly
code in apps/ will become Forth code. The concept of an assembler code library
will become obsolete.
However, Forth's core use some of that code. To facilitate the transition, I'm
inlining that code directly in Forth's code.
My approach with RS was slightly wrong: RS' TOP was always containing current
IP. It worked, but it was problematic when came the time to introduce
RS-modifying words: it's impossible to modify RS in a word without immediately
messing your flow.
Therefore, what used to be RS' TOS has to be a variable that isn't changed
midway by RS-modifying words. I guess that's why RS is called *return* stack...
Big one.
This allows us to write higher order words directly in Forth, which is much
more convenient than writing post-immediate (see "NOT" structure in diff if
you want to see what I mean) structures in ASM.
These structures can then be written to ROM (rather than loaded in RAM for
definitions loaded at run-time).
That's quite a bit of tooling that was added, 2 compilations stages, but I
think it's well worth it.
