Distinguish log from information

[Tygre]

Currently, when generic modules, like FTP, need to communicate information, they use the logging mechanism (log_print_debug) instead of a proper communication channel.

[Tygre]

https://stackoverflow.com/questions/2031163/when-to-use-the-different-log-levels

1. DEBUG: for debugging purposes
2. INFO: for information (and debugging)
3. WARN: potential problem
4. ERROR: recoverable problem
5. FATAL: unrecoverable problem

[Tygre]

Changed a lot log.h and log.c to allow these five levels of logging and also make the code cleaner.