first steps towards bytecode scripting
replace old script code
replace arb with _
update spec
update bytecode to operate on generic 64-bit values
add floating point operations
rename y (byte) -> v (value)
add divide by zero checks
add maximum stack size

this may wind up being unnecessary if MaxInstructions stays
less than MaxStackLen; simple op_push calls won't be capable
of overflowing the stack before execution ends. However, there
may be other ways of populating the stack without exceeding the
MaxInstructions limit.
better resource management

resource pools are now checked prior to instruction execution.
Cost is the only resource currently checked, but more will likely
be added in the future.
export SaveScript and LoadScript
return of the ScriptInput
update participant functions for ScriptInput
call LoadScript in compile
update tests for new bytecode spec
fix some resource bugs
fix bootstrapping opcode
add nil script test
change boolean sentinel to struct{}
add xfer opcode and genesisScript