These APIs take size parameters, which can be used to properly bounds-check the
inputs and outputs for various registers. Additionally, all backends now throw
UC_ERR_ARG if the input register numbers are invalid.
Completes #1831.
quit_request is for internal use. This means the IP register was updated and
qemu needs to rebuild the translation blocks.
stop_request is set by the user (uc_emu_stop) to indecate that unicorn sould
stop emulating.
