add fastjson library and test classes

build.gradle

@@ -26,6 +26,9 @@ dependencies {
 	// Fabric API. This is technically optional, but you probably want it anyway.
 	modImplementation "net.fabricmc.fabric-api:fabric-api:${project.fabric_version}"
 
+	// Serialization
+	compile group: 'com.alibaba', name: 'fastjson', version: '1.2.56'
+
 	// PSA: Some older mods, compiled on Loom 0.2.1, might have outdated Maven POMs.
 	// You may need to force-disable transitiveness on them.
 	dependencies {

src/main/java/com/josyf/macrobuttons/ConfigFile.java

@@ -0,0 +1,4 @@
+package com.josyf.macrobuttons;
+
+public class ConfigFile {
+}

src/main/java/com/josyf/macrobuttons/Message.java

@@ -0,0 +1,4 @@
+package com.josyf.macrobuttons;
+
+public class Message {
+}