offer choice of all log levels

[rade]

We use four log levels in our code - debug, info, warn, error - yet only allow selection of "all except debug" (the default) and "all" (when -debug is supplied).

[inercia]

I think warn and error should never be silenced, right?. I cannot imagine a situation where you don't want to see errors. If this is the case, that would leave info and debug as optional. Maybe we could -verbose/-v for enabling info, and a second -v or -debug could enable debug...