extend parsing instructions to use json object instead of plain txt (#929)

testdata/json-data-format-var-naming.go

@@ -0,0 +1,8 @@
+package fixtures
+
+func foo() string {
+	customID := "result"    // ignore
+	customVm := "result"    // json:{"MATCH": "var customVm should be customVM"}
+	CUSTOMER_UP := "result" // json:{"MATCH": "don't use ALL_CAPS in Go names; use CamelCase", "Confidence": 0.8}
+	return customId
+}