Added G30 as optional position for tool change.
Moved new tool change mode from PR#673 to $346 - Tool change options.
Moved Modbus RTU code from spindle plugin to the core.
Fixed bug in delayed task handler, might occasionally hang the controller.
Added 5s timeout/abort handling when waiting for index pulses prior to startiong spindle synchronized motion.
Added definitions for M401 (deploy probe) and M402 (stow probe) for plugin use.
Added support for probe protected message and alarm. Requires driver support for interrupt handled probe input.
