International LT engines sound fix for ATS

This mod gives sound improvements from the A26 and S13 engines for the International LT truck, with more realistic sound curves. This mod is functional for the American Truck Simulator game, for versions 1.44 to 1.50 (it can also be functional for Euro Truck Simulator 2 if you have the International LT truck with the same definition). This mod doesn't replace the default engines in the game, it has its own engines with independent sounds with more realistic audio curvatures and distancing improvements.