Feature/defaults

A simple method for configuring pins which need to be initialized at startup, but don't need to be touched thereafter.

Example configuration:

default.alpha_ms1_pin           10.29!
default.alpha_ms2_pin           10.30
default.alpha_ms3_pin           10.31!

Sets the mode select pins for the alpha axis to 0b101, for 32 micro-steps.
I think you're right - needs to be !cs