v68k:  Downgrade emulator to processor_state
[NEW] v68k-utils:  Add load_file()
v68k-callbacks:  Factor out to load_file()

Let load_file() do the heavy lifting of actually opening and reading the
file, and focus on the details of wiring that into emulated memory space
in load_callback().
xv68k:  Use load_file()
Merge branch 'load_file'