independent flag for json structured logging

- logjson flag remove logformat flag
- passed to eth Config
- logsystem not a field of Ethereum
- LogSystem does not need to expose GetLogLevel/SetLogLevel
- message struct just implements more generic LogMsg interface
- LogMsg is a fmt.Stringer with Level()
- jsonMsg ([]byte) implements LogMsg
- remove "raw" systems
- move level logic inside StdLogSystem
- logsystems only print their kind of msg: jsonLogSystem prints jsonMsg, StdLogSystem prints stdMsg

logger/log.go

@@ -18,7 +18,7 @@ func openLogFile(datadir string, filename string) *os.File {
 	return file
 }
 
-func New(datadir string, logFile string, logLevel int, logFormat string) LogSystem {
+func New(datadir string, logFile string, logLevel int) LogSystem {
 	var writer io.Writer
 	if logFile == "" {
 		writer = os.Stdout
@@ -27,14 +27,22 @@ func New(datadir string, logFile string, logLevel int, logFormat string) LogSyst
 	}
 
 	var sys LogSystem
-	switch logFormat {
-	case "raw":
-		sys = NewRawLogSystem(writer, 0, LogLevel(logLevel))
-	case "json":
-		sys = NewJsonLogSystem(writer, 0, LogLevel(logLevel))
-	default:
-		sys = NewStdLogSystem(writer, log.LstdFlags, LogLevel(logLevel))
-	}
+	sys = NewStdLogSystem(writer, log.LstdFlags, LogLevel(logLevel))
+	AddLogSystem(sys)
+
+	return sys
+}
+
+func NewJSONsystem(datadir string, logFile string) LogSystem {
+	var writer io.Writer
+	if logFile == "-" {
+		writer = os.Stdout
+	} else {
+		writer = openLogFile(datadir, logFile)
+	}
+
+	var sys LogSystem
+	sys = NewJsonLogSystem(writer)
 	AddLogSystem(sys)
 
 	return sys