PWM updates; Servo fixes

Servo pulse range: 600-2400μs determined by testing the following:

- Hi-Tec HS-55
- Hi-Tec HS-311
- Hi-Tec HS-322HB
- Hi-Tec HS-485HB
- Hi-Tec HS-422
- Hi-Tec HS-645MG
- Hi-Tec HS-755HB
- Hi-Tec HS-805BB
- Hi-Tec HS-5685MH
- Hi-Tec HSR-1425CR
- EMAX ES08A11 II
- Futuba S3003
- Tower Pro MG995
- Power HD 1501MG
- Parallax Continuous Rotation
- Parallax High Speed Continuous Rotation