Consider putting C stack below $2000

[gardners]

CC65 on the C64 is a bit annoying in that it puts the C stack at $0800. They do it so that the one-time-initialisation code gets overwritten and that space reused. But it means you can't run a CC65 compiled program more than once, without reloading it. On the C65/M65 in C65 mode there is free memory from $1300 or so to $1FFF, where the stack could be placed, allowing a programme to be run more than once.

BTW - Nice work on getting the basic memory model running :)