doc updates, and relabel ReportMethod

in the Logrus context it's the caller, so use that internally.  Label
stays as 'method' since in the context of the log event that seems more
correct.

json_formatter.go

@@ -12,7 +12,7 @@ const (
 	FieldKeyMsg    = "msg"
 	FieldKeyLevel  = "level"
 	FieldKeyTime   = "time"
-	FieldKeyMethod = "method"
+	FieldKeyCaller = "method"
 )
 
 func (f FieldMap) resolve(key fieldKey) string {
@@ -34,7 +34,7 @@ type JSONFormatter struct {
 	// 		 FieldKeyTime:   "@timestamp",
 	// 		 FieldKeyLevel:  "@level",
 	// 		 FieldKeyMsg:    "@message",
-	// 		 FieldKeyMethod: "@caller",
+	// 		 FieldKeyCaller: "@caller",
 	//    },
 	// }
 	FieldMap FieldMap
@@ -62,8 +62,8 @@ func (f *JSONFormatter) Format(entry *Entry) ([]byte, error) {
 	data[f.FieldMap.resolve(FieldKeyTime)] = entry.Time.Format(timestampFormat)
 	data[f.FieldMap.resolve(FieldKeyMsg)] = entry.Message
 	data[f.FieldMap.resolve(FieldKeyLevel)] = entry.Level.String()
-	if ReportMethod() {
-		data[f.FieldMap.resolve(FieldKeyMethod)] = entry.Method
+	if ReportCaller() {
+		data[f.FieldMap.resolve(FieldKeyCaller)] = entry.Caller
 	}
 	serialized, err := json.Marshal(data)
 	if err != nil {