ForgeWrapper

Allow MultiMC to launch Minecraft 1.13+ with Forge.

How to use

Download Forge installer for Minecraft 1.13+ at [https://files.minecraftforge.net/].
Download ForgeWrapper jar file at the release page.
Run the below command in terminal:
```
java -jar <ForgeWrapper.jar> [--installer] <forge-installer.jar> [--instance <instance-path>]
```
Notice: If you don't specify a MultiMC instance path, ForgeWrapper will create the instance folder in current working space.
If the instance folder which just created is not in MultiMC/instances folder, you just need to move to the MultiMC/instances folder.
Run MultiMC, and you will see a new instance named forge-<mcVersion>-<forgeVersion>.