stick sensitivity

[briaguya-ai]

i know there was discussion of something more robust than this to handle deadzones for ess or a "move the control stick in a circle to find the range" solution, but this is a simple way to make it so people can use n64 controller adapters that don't provide a full range to sdl (which doesn't respect range calibration using jstest on linux because of some evdev stuff that gets real messy to try to fix as a user)

the mapping string matches another adapter, so it won't make it into the upstream gamecontrollerdb, but the one i used to test was

030083a08f0e00001330000010010000,Mayflash N64 Adapter,a:b1,b:b2,start:b9,leftshoulder:b6,leftstick:-a1,rightstick:-a2,dpup:h0.1,dpleft:h0.8,dpdown:h0.4,dpright:h0.2,lefttrigger:b8,righttrigger:b7,platform:Linux,