Adding Support for Turbo button

[DarkCTO]

Hi, a shortcut on keyboard and gamepad to support Turbo.
That is, repeatedly performing a button. This is great to avoid cramps and much more enjoyable.

Example: Turbo + A key => will set A to be Turbo'ed, holding A will be the same as pressing A repeatedly rapidly.

[DarkCTO]

Same request on EmulatorJS I think WebRCade is based on ?
https://github.com/emulatorjs/emulatorjs/issues/1077