Build system working on DOS; add necessary scripts and documentation

Build system working on DOS; add necessary scripts and documentation

Unfortunately, the resulting programs don't actually /run/ correctly
on DOS yet, but rather crash with SIGILL (at _ick_resize plus 3 bytes).
I suspect this is linked to the bool-with-varargs problem somehow.
There's also a problem with clock slew / failure to restore timestamps
when building without yacc/lex, which needs fixing (and unfortunately,
adding a few uses of "touch" doesn't seem to work on DOS for some
reason).