Error messages are written to stderr whilst normal terminal output is stdout.
When redirecting output to pipelines or files these two streams can get
separated as they are buffered separately. To avoid this, term.c now provides
a function terminal_message() that works just like avrdude_message() but
flushes stderr and stdout before printing on stderr, and it flushes stderr
afterwards.
This commit replaces all avrdude_message() calls except for progress report
with terminal_message() to ensure stdout and stderr streams keep together.
This enables the new quell terminal command to switch on and off progress
reports to the terminal. The code for this was moved from main.c to term.c.
It can be used as library call for other frontends than main.c
Stefan Rueger
MCUdude
Marius Greuel