For systems supporting only a single button, the turbo-button will toggle firing that button without the need to hold it.
When holding the button turbo will be suspended and resumed when the button is released. Holding the button may have a different function to just tapping it, e.g. charging the beam in R-Type on C64/Amiga.
The original implementation in RA is named 'Classic' because I have no
idea where it originates from.
* Refactored the way RetroArch sets the input state/poll callbacks, hopefully it's clearer now.
* The unnamed enum of poll type behaviors in core.h was moved to retroarch.h and is now named rarch_poll_type.
It represents polling behaviors implemented specifically by RetroArch.
First element starts at 1 to match the data encoding of RETRO_ENVIRONMENT_POLL_TYPE_OVERRIDE.
* Created rarch_set_input_cbs - sets different input state/poll callbacks based on a
rarch_poll_type parameter.
* Replaced the static variable core_poll_type_override in retroarch.c with a poll_type_lock flag
inside global_t's menu struct;
RETRO_ENVIRONMENT_POLL_TYPE_OVERRIDE will now call rarch_set_input_cbs and set poll_type_lock,
which blocks the user from changing behaviors from the menu.
* To follow the RETRO_ENVIRONMENT_POLL_TYPE_OVERRIDE spec, we now set poll_type_lock and call
rarch_set_input_cbs after calling unload_game.
* core_set/unset_netplay_callbacks will now set/unset poll_type_lock, preventing the
poll type from being changed by the user;
* The MENU_ENUM_LABEL_INPUT_POLL_TYPE_BEHAVIOR action will now call rarch_set_input_cbs if poll_type_lock
isn't set, which means poll type is changed on-the-fly.
