add complete documentation

Hey.

It would be nice if there was something like a write_to_stdout() function, or if write_to_textfile() would somehow allow writing to stdout.

For debugging that would seem to be much more helpful. Also, distros may have their own unified means of collecting the .prom files and thus even in production it may make sense to let a program simply write the metrics to stdout.

Cheers,
Chris.

PS: Using /dev/stdout doesn't work, as it tries to write it's tmpfile there.

Iniziare individuando write_to_textfile() e verificando come gestisce il caso /dev/stdout. Determinare il comportamento previsto per la scrittura diretta delle metriche su stdout, preservando l'output esistente su file, quindi verificare che entrambi i percorsi di output funzionino come previsto. Nell'issue non sono indicati file o test.