Low frequency to control stepper motors

[padmalcom]

Hi, thanks for the board, very nice idea!

I'm facing the issue with a very slow moving stepper motor. If I follow your pwm example, the stepper (with an tb6600) moves very slow. I tested each setting from the tb6600 and changed frequencies. Only if I don't allow a delay at all between the pulse high and low, the stepper moves in a good speed. That is fine, but this does not allow me to slow it down.

I saw there is a pull request that enables PWM for your GPIO module. Maybe you can merge it?

[ChristopherRush]

@padmalcom I have merged the pull request.