Add support for second SD card on SPI bus for Duet WiFi including
implementation of M21 and M22
New temperature monitoring
Increased PWM resolution
When uploading files to wifi module, skip empty blocks
Revised TMC driver in preparation for standstill current reduction
Fixed PrintMonitor bug when the slicer comment includes a '\' character
1. Changed thermocouple/RTD support to use new (fixed) version of
SharedSpi in CoreNG
2. PrintMonitor fixes:
- Speed up getting file info, because it was slow enough to cause Ajax
timeouts on some systems
- Reduce the number and volume of messages printed when debugging was
enabled, and send them only to the USB interface, because it was
overloading the message buffer system and causing Ajax errors
- Added separate time stats for file seeks
Changed to CoreNG
Implemented chrishamm's latest Network and Webserver changes, including
Telnet streaming
Added S parameter to M997 command for DuetNG
Increased file read block size to 2K when getting file info
