Support R and S parameters in M109 and M190 as Marlin does
Added support for M191
Added support for Steinhart-Hart C parameter
Thermistor disconnected threshold now depends on thermistor parameters
Added I parameter in M280 command
Added diagnostic test (M122 S101) for SX1509B chip on Duet WiFi
expansion boards
Heaters driven from TC channels on Duet WiFi no longer glitch on for a
short while after reset
Bug fix: M280 S-1 was ignoring inverted output status
Bug fix: if there were too many files in the /gcodes folder then AJAX
errors occurred (thanks chrishamm)
Initialise all heater model parameters in constructor so that on a Durt
0.8.5 heater 6 has sensible model parameters even though it is disabled
Fixed PWM frequenct on Duet 0.6/0.8.5
Fixed several bugs in file time stamping
Fixed M280 and M42 commands using unused heaster channels on Duet 0.6
and 0.8.5
Reduced the amount of I2C traffic, by using DueX5 interrupt line to tell
if new data is available and by only sending fan PWM values when they
change
Display TMC2660 driver status and DueX2/X5 stall status in M122 response
Removed E parameter from M574 command (use M558 I parameter instead)
Fixed response to M307 with H parameter only
