cleaned up settings.h
improved some defaults
clamped safe speed to 100% of nominal speed. Fixes a problem that might have spelled trouble at very low feed rates
removed inline-keywords because gcc ignores them anyway
circle buffers now power of two size and indicies are unsigned to help gcc make a few nice optimizations
renamed serial_protocol -> protocol
renamed protocol methods to reflect the new module name
refactored handling of settings '$' command out of gcode module and into settings module
lowercased boolean constants
cleaned up handling of number parsing in settings_execute_command
formatting
spindle operations are now synchronized
made most internal function static to allow gcc to inline them
added support for limit switches and homing action
acceleration-Grbl now works with atmega 168 by disabling arc motion
stepper enable pin now toggles to reflect the active/passive state of the stepper subsystem
added support for G92
result of G92 also affects planner
fixed a double rounding error compensation bug in mc_arc thanks to Etienne Chové
added missing line from G92 patch