stack_machine: code cleaups
machine: add acs_register_user_function()
stack_machine: add print function
stack_machine: add acs_init() as global initializer
stack_machine: revise call ops
stack_machine: stubize acs_call()
stack: introduce call_instance()
stack: add basic test
stack: add opcode strings
value: fix sanity check in value_copy()
stack: add dumps of stack and pc in execute()
stack: fix value setup in acs_register_user_function()
stack: add dumps for testing