AdvancedFirmata based asynchronous stepper motor control
implemented using functionality defined in https://github.com/jgautier/firmata/pull/25
fixed formatting, pin referencing, and scoping to remove "self"
added check for advanced firmata firmware
added examples, minor code tweaks
Refactoring Stepper code

- Allow an array of pins (in addition to object)
- Create reasonable defaults where possible
- Adds stepper-sweep example
- General code refactoring

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>