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.

entry.go

@@ -46,7 +46,7 @@ type Entry struct {
 	Level Level
 
 	// Calling method, with package name
-	Method string
+	Caller string
 
 	// Message passed to Debug, Info, Warn, Error, Fatal or Panic
 	Message string
@@ -135,8 +135,8 @@ func (entry Entry) log(level Level, msg string) {
 	entry.Time = time.Now()
 	entry.Level = level
 	entry.Message = msg
-	if ReportMethod() {
-		entry.Method = getCaller()
+	if ReportCaller() {
+		entry.Caller = getCaller()
 	}
 	if err := entry.Logger.Hooks.Fire(level, &entry); err != nil {
 		entry.Logger.mu.Lock()