Merged in zpl's changes. The FTP server is not yet reliable, in
particular trying to delete a file via FTP after copying another may
result in the Duet rebooting due to the webserver module getting stuck
in a spin loop. Also the copied file has on one occasion been observed
to be shorter than the original.
Improved speed of response to M220 command
Limit length of text returned in response to rr_name web command, stop
on first control character, and escape and quote or backslash characters
Changed network startup to avoid long delay if no network cable is
connected
Enable DHCP support if IP address is configured as 0.0.0.0 (not working
yet)
Move thermistor parameters to M305, added parameter to configure series
resistance
Added B and W PID parameters
Changed webserver and network code to support multiple concurrent
connections
Removed support for differential-mode ultrasonic z-sensor
Reduced X and Y instantDv from 15 to 10 mm/sec to allow outlines of
holes to e drawn at lower speed
Changed temperature reading code to give thermistor disconnected reading
of -273C when there is a negative high ADC offset correction
Increase TCP window size from 1 to 2 packets and increase maximum amount
of web data sent to 1460. This decreases the page load time fro a
Windows client fro 6 seconds to less than 1 second. It also fixes a
problem whereby when using a Ubuntu client, file upload and direct print
didn't work unless the reprap.js file was edited to reduce the maximum
amount of data sent per request. Also we now initialize unused memory
with known data so that in response to the M111 S1 command we can better
estimate the amount of free memory.
