Simple Sprint for OpenMW

Press Alt/Shift/Use/Activate key while running to gain boost to speed, sprinting results in higher fatigue use. Sprinting only works when running forward, doesn't work when sneaking, swimming sprint is optional. The only limit to sprinting time is your fatigue. Another optional way to start sprinting is double tap Forward key in limited time period, by default 0.5s. Speed bonus, additional fatigue drain and verbose mode are configurable in script options. Bonus to speed is calculated as base_bonus + athletics / 4. Fatigue drain happens every 0.1s when sprinting and is calculated as base_fatigue + athletics / 50. Default base_bonus = 50, base_fatigue = 1. More fatigue drain when sprinting with ready weapon.