Added experimental support for G66 (modal macro call) and G67 (end modal macro call).
Made axis letter to axis/motor assignment for axes ABCUVW freely changeable at compile time.
Fix for some G65 arguments being incorrectly validated for normal use (sign, range).
Added repeat support to G65 macro call via the optional L parameter word.
Changed default setting for ABC-axes to rotary.
Changed defaults for jerk settings to 10x acceleration settings.
Disabled jerk for jog, probe and spindle synchronized motion.
Added _active_probe system parameter, returns -1 if no probe inputs available.
Minor bug fix, G5.1 and G33.1 motion commands were not coverted to the correct string equivalent in $G output.
Added lightweight JSON serializer outputting directly to file.
Fix for event handler sometimes called too early. Ref. issue #818.
For developers: added optional device filing system that can redirect file read/write to serial streams.
