move all the files in the root directory so this can be compiled with grbl.
I use LINUX to test with.
Variable spindle speed need these registers, I'm not 100% sure if the intergers are right.
This is needed for a debug print function that in never called.
Looks like get_dirction_mask is now get_direction_pin_mask.
Looks like rx_* functions are now serial_rx_* functions.