Change the CODE macro used in the kernel and in NEXTOR.SYS
so that it doesn't rely anymore in the assembler being able
to assemble 8080 mnemonics.

- Re-encode in UTF-8
- Add .strenc instructions
- Remove redundand macros
- Adjust makefile

These files are data.mac, drv.mac, kbar.mac, chgbnk.mac, rel.mac

Also, makefile adjusted appripriately.

With this, M80 isn't needed anymore to assemble the Nextor kernel
(sjasm is still needed)

- Replace data structures with macros and modules.
- Replace multi-push and pop with single ones.
- Replace "ld iy,de" with real instructions.
- Replace 512 repetitions of LDI with a REPT.
- Replace $ hex prefix with h suffix.
- Expect MASTER_ONLY to be defined externally.

The original code seems to mistakenly assume that "pop x,y,z"
generates "pop x - pop y - pop z" when actually what sjasm generates
is "pop z - pop y - pop x"; surprisingly, the driver seems to work
fine with and without fixing this. So in this commit these are fixed,
but if a BAD_POPS constant is defined then the wrong pops will be
generated instead (may be useful for debugging/testing).

Additionally, the makefile has been adapted accordingly.

Also adjust Makefile to properly assemble it.

Also keep it "old style" by removing escape sequences and DZs

Also change --status-verbosity to --verbosity in makefiles

Also add an explicit program name instruction to all source files.

….mac for readability

- Update README to mention Nestor80 instead of M80.

Also update README to point out that SDCC 4.2 or newer is now required.