Detecting IGRs double reset in pair mode

[borti4938]

In pair mode the SuperCIC doesn't translate a double reset into a long reset. Hence, it has to be detected by the sd2snes. Detecting double reset is not a problem. The normal reset (combination L+R+Sel+Start) becomes a problem as a game resets while combination is pressed and hence the reset is retriggered if the games turn on automatic joypad read...

Some ideas from #44 :

• timeout, where no further reset pushes are allowed to occur after the second push (currently implemented in develop branch, but buggy)
• sd2snes pulls the reset line once a reset push is detected and releases just before reading the reset line again (dirty)
• Hijacking reset vector (might be difficult)
• Inject NOPs -> add an FPGA command that will cause the data lines to always return $EA when read (a bit overkill)

[mrehkopf]

IIRC I was ultimately going to implement this using an interrupt hook which will be required for sd2snes-side WRAM cheats and IGR functionality anyway. The sd2snes itself would then detect the keypress combination and act accordingly. But that's still some way to go.

[borti4938]

tested the version, where sd2snes pulls and releases the reset line once a short reset was detected. works reliable with all games I tested so far :) See commit a5ead0a