Extra turbo options

Patch adds new options for turbo, only available with extended physics: LUT for gas pedal and spin delay.

[TURBO_0]
LAG_DN=0.985
LAG_UP=0.9965
MAX_BOOST=1.0
WASTEGATE=0.58
DISPLAY_MAX_BOOST=0.58
REFERENCE_RPM=2500
GAMMA=4
COCKPIT_ADJUSTABLE=0
EXT_GAS_CURVE=(|0=0|0.3=0|1=1|)
EXT_SPIN_DELAY=0.2

Generally, gas pedal is used as a multiplier for turbo activation. With EXT_GAS_CURVE (which could also be a file name instead of inline LUT), you can remap that multiplier value, for example, stopping turbo from activating until pedal is pressed to at least 30% of its range. Somewhat similar effect could be achieved with controller with INPUT=GAS, but LUT allows to alter value before gamma is applied. Default value (for original physics) is EXT_GAS_CURVE=(|0=0|1=1|).

As for EXT_SPIN_DELAY, it adds some sort of negative turbo pressure, extending boost range. Engine would act as naturally aspirated until turbo would spin beyond zero point. With EXT_SPIN_DELAY=1, if original turbo boost would equal 0.5, after altering, it’ll drop to 0, and would climb from there. With EXT_SPIN_DELAY=0.5, it would be 0.33. Default value (for original physics) is EXT_SPIN_DELAY=0.

Thanks to dj_amur for the suggestion of adding it.