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_test.go

@@ -170,8 +170,8 @@ func TestJSONTimeKey(t *testing.T) {
 	}
 }
 
-func TestFieldDoesNotClashWithMethod(t *testing.T) {
-	SetReportMethod(false)
+func TestFieldDoesNotClashWithCaller(t *testing.T) {
+	SetReportCaller(false)
 	formatter := &JSONFormatter{}
 
 	b, err := formatter.Format(WithField("method", "howdy pardner"))
@@ -186,12 +186,12 @@ func TestFieldDoesNotClashWithMethod(t *testing.T) {
 	}
 
 	if entry["method"] != "howdy pardner" {
-		t.Fatal("method field replaced when ReportMethod=false")
+		t.Fatal("method field replaced when ReportCaller=false")
 	}
 }
 
-func TestFieldClashWithMethod(t *testing.T) {
-	SetReportMethod(true)
+func TestFieldClashWithCaller(t *testing.T) {
+	SetReportCaller(true)
 	formatter := &JSONFormatter{}
 
 	b, err := formatter.Format(WithField("method", "howdy pardner"))
@@ -206,14 +206,14 @@ func TestFieldClashWithMethod(t *testing.T) {
 	}
 
 	if entry["fields.method"] != "howdy pardner" {
-		t.Fatalf("fields.method not set to original method field when ReportMethod=true (got '%s')",
+		t.Fatalf("fields.method not set to original method field when ReportCaller=true (got '%s')",
 			entry["fields.method"])
 	}
 
 	if entry["method"] != "" { // since we didn't actually log, it's set to the empty string
-		t.Fatalf("method not set as expected when ReportMethod=true (got '%s')",
+		t.Fatalf("method not set as expected when ReportCaller=true (got '%s')",
 			entry["method"])
 	}
 
-	SetReportMethod(false) // return to default value
+	SetReportCaller(false) // return to default value
 }