New firmware 1.09b-dc42 for Duet electronics

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Z axis min and max limits are now enforced if the axes have been homed. On a delta, the Z max limit is ignored because the homed height is used as the limit instead.
Following 6- or 7-factor auto-calibration, the M665 command now shows the re-calculated delta radius instead of the configured delta radius, and also the X and Y tower angular offsets.
When delta auto-calibration is run, the before and after RMS errors are shown .
Pause/resume now works when absolute extruder coordinates are used. The behaviour is not perfect, and relative extruder coordinates are still recommended if your slicer can generate them.
The maximum length of the SD card file listing that can be sent to PanelDue has been doubled.
Implemented zpl's Network changes (thanks zombiepantslol)
Implemented zpl's PrintMonitor changes including M404 command and experimental Kisslicer support (thanks zombiepantslol)
Increased the default maximum instantaneous X and Y speed changes from 10 to 30mm/sec.
The web interface on the SD card image is now DuetWebControl 1.06.
Modified all resume.g files to set the speed when moving to the paused head coordinates.
When the Move code runs out of moves, if ancillary PWM was in use then it is set to zero. This is as a safety precaution e.g. when the Duet is being used to control laser engraver.
To put the board into programming mode, the M999 command now requires parameter PERASE instead of S4321.
Bug fix: if M226 was used to pause the print, the resume coordinates were not set up correctly.
Bug fix: when changing the travel direction, the head was sometimes slowed down more than necessary.
Bug fix: warm-up time was not shown correctly in DuetWebControl.
Bug fix: extruder drive positions were always shown as 0.0 in DuetWebControl.
Bug fix: incorrect PID parameters were returned in response to M301.