Also, removed leftover in runbin.c (what did it do there??) that
could result in tests falsely passing.

This should make tests a bit more convenient to write and debug.

Moreover, begin de de-IX-ization of parseExpr. I have, in a local WIP, a
parseExpr implemented using a recursive descent algo, it passes all tests, but
it unfortunately assembles a faulty zasm. I have to find the expressions that
it doesn't parse properly.

But before I do that, I prefer to commit these significant improvements I've
been making to tests harness in parallel of this development.

Will be much much easier to tests new core routines without having to
re-create their context first.

Also, extract parse.asm from core.asm