compile-time ffi w/o sigs yet

sleep = extern sleep(n=n)
sleep(0.1)
extern: !dlsym just warns, create manual proto

no wrapper yet, not in the VM yet, just at compile-time
extern: add sample, start with arg handling
extern: add WITH_EXTERN config.h. not with SANDBOX

fix example
extern: simplify extern creation with calloc

add a return op to the generated asmb (not yet working)