Dynamically change log level in the file

Hi,

Thanks again for logforth.

I wonder if I can enable log for a file, i.e. at the top of the file I want to say `log_level!(DEBUG)`, so it will add to the global configuration.

I understand that I can change that at env level, or when I init the log, but when we have lots of files, it is difficult to get the correct module of the file to enable the log.

Thanks,