Reduced block read size when retrieving file info to work around an
intermittent bug that causes the SDHC card/ FATfs stack to return data
from the wrong sector sometimes. Tidied up some other code.
Added new variable "extr" in Json response to report extruder positions
Added new fileinfo request type, returns file size, object height, and
total filament needed (if available)
Fixed bug in returning last command response in Json response
Disable interrupts when adding/removing network request structs from
linked lists, in case lwip does callbacks from ISR contexts
Completed changes to support multiple concurrent HTTP file requests.
Added support for new poll response for future support of additional
heaters and multiple extruders. Fixed a bug in reporting extruder
distance.
Removed file httpd.c and moved its functions into Network.cpp. This
gives us type-checking across more interface boundaries and eliminates a
number of global functions. Also removed unused files fs.c, fsdata.c,
httpd-original.c.
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
