The idea is to have the host ping the printer periodically with a M79 to
enable certain features/UI. Using the usb_timer is not a good solution
for this as it depends on seeing a 'G' character
The LCD code, or whatever code is implementing the new functionality
will need to include host.h and check whether M79_timer_get_status()
returns 0 (timer not running) or 1 (timer is running).
I created a new file for the code host.cpp which we can use to expand
host related functionality and not clutter Marlin_main.cpp further.
Change in memory:
Flash: +104 bytes
SRAM: +5 bytes
gudnimg