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.
Parking mode improvements.
Removed requirement for external encoder for spindle sync if stepper spindle is enabled.
Improved handling of $680 stepper enable delay.
Added ADC/DAC resolution to $pinstate command, changed reported values to integer for ADC/DAC devices and float formatted for PWM devices.
Numeric settings can now be set via G65P1Q<n>S<value>, <n> is the setting number, <value> is the new value.
Changed alarm code for Modbus exceptions (communication errors) from 14 to 19.
Refactored MPG stream code to allow plugins to hook into MPG streams (via event handler).
Added _free memory system parameter, returns value in KBytes or -1 if not available from driver.
Changed basic stream data type from char to uint8_t, added HAL function and core API for releasing/closing UART streams.
Added '$709' setting for second PWM spindle when available - PWM options.
Added properties to PWM spindles to allow "overdriving" PWM output when _RPM controls spindle enable signal is enabled with '$9' or '$709'.
Optimized Modbus CRC calculation, may fix issue with a compiler generating different code compared to most others. Ref. issue #723.
Now returns no data for alarm and error enums when firmware is compiled for 128K versions of the STM32F1xx MCU.
This frees up some flash space for plugins etc.
