ClawController prone to out or range or invalid servo values

[kevinjwalters]

The ClawController aims to drive the servo between 90 and 180 degrees but

• the code only uses map and does not use constrain to guarantee the values are within that range
• the code has overflow issues with 16bit arithmetic (Arduino Uno int is 16bit) on a large buffer of ADC values

Another improvement is to use float for the envelop function/variable to avoid the coarse conversion for integer based Arduino map.