Rework pkg/log, add 'loglevel' and 'logdate' flags, streamline

- removes some previously added manual location strings: now handled by pkg/log depending on loglevel
- kept manual string locations on fmt print functions
- add 'notice' and 'critical' loglevels
- add 'Panic' and 'Panicf' functions to log panics
- adresses issue #26

pkg/archive/nodelist.go

@@ -64,7 +64,7 @@ type NLExprIntRange struct {
 
 func (nle NLExprIntRange) consume(input string) (next string, ok bool) {
 	if !nle.zeroPadded || nle.digits < 1 {
-		log.Error("ARCHIVE/NODELIST > only zero-padded ranges are allowed")
+		log.Error("only zero-padded ranges are allowed")
 		return "", false
 	}