add routines for 1-pwm in driver code

[runger1101001]

Add initial support (api and generic implementation only so far) for 1-pwm in the driver code.

1-PWM is not useful for BLDC or stepper control, but has other applications connected to our library:

• DC Motor control (stay tuned for new stuff in the drivers library)
• Active and regenerative braking
• PFC (power factor correction)
• and of course it can be used to dim the headlights of your robot :-D

[askuric]

You're right, this is a good extension.

[runger1101001]

:-) I'll merge it... I'll try to add some hardware driver implementations in the weeks to come, but first I will test the power-shield