MPH and FPS not recognized as units

[emroch]

Miles per hour and feet per second must be spelled out as "miles/hour" or "mi/h". This is normal for metric folks - kilometers per hour is usually km/h - but imperial speeds are usually specified as mph. Feet per second is probably less common, but as long as we're changing mph, we might as well throw in fps too.

[wolph]

I have to say that I'm a bit in doubt about the fps because it's more commonly used for frames per second, but I suppose it will work for now :)

I've updated the code to include these