Add {username} token

Closes #8

src/main/java/chylex/customwindowtitle/data/CommonTokenData.java

@@ -8,6 +8,7 @@ public final class CommonTokenData {
 	public static void register(final CommonTokenProvider provider) {
 		registerToken("mcversion", noArgs(provider::getMinecraftVersion));
 		registerToken("modversion", oneArg(provider::getModVersion));
+		registerToken("username", noArgs(provider::getUsername));
 	}
 	
 	private CommonTokenData() {}

src/main/java/chylex/customwindowtitle/data/CommonTokenProvider.java

@@ -1,6 +1,7 @@
 package chylex.customwindowtitle.data;
 
 import net.minecraft.SharedConstants;
+import net.minecraft.client.Minecraft;
 
 public interface CommonTokenProvider {
 	default String getMinecraftVersion() {
@@ -8,4 +9,8 @@ public interface CommonTokenProvider {
 	}
 	
 	String getModVersion(final String modId);
+	
+	default String getUsername() {
+		return Minecraft.getInstance().getUser().getName();
+	}
 }