This adds a test program which can be loaded and executed by the host.
It simply returns a value in the `a` register.
The linker script is modified so that it will output an o65 file, and
the memory sgments are changed as well. There is no STARTUP segment
defined, so it uses the default `none` crt0, which sets up the stack
and does initialization and deconstruction.
The Makefile is modified to not turn the output into an intel hex file,
and instead keep it as the o65 file.
