Basic: move logic/release stack to $C000

Basic: move logic/release stack to $C000

Uses stack PUSH*/POP*/PEEK* routines instead of direct X% and Y%
access. Seems to be about the same performance (maybe a 5% performance
hit at most).

This gives us a larger stack (1920 2-byte words of $C000 rather
than 200 words as before). The release stack at $CF00 stays the same
size (64 4-byte addr/level entries).

Also saves over 1K or program and array space. So take the opportunity
to expand Z% entry space from 3712 to 3950.