New library: Motor driver API for L293D shield v1 ... (request for comments)

Apologies if this is not the right forum to present my own code.

I rewrote the code from into a C++ Class API, which reduced the code size (not counting the Servo library) from 2,8 KB + 224 bytes to 1,5 KB + 11 bytes (one motor example) or 1,9 KB + 23 Bytes (4 motors example).

Thus I decided to upload it and ask for your opinions and suggestions.

For now, everything is still in one .h file. I'm planning to change that, and also to change the names to CamelCase. (What's best: "PWM_Pin", "PWMPin" or "PwmPin"?)

The DC motor functions are tested to the extent used in the examples (set direction and speed), the unipolar motor connections will be tested later. I don't have step motors yet.