1.12 version not compliant with Forge's coremod guidelines

[josephcsible]

The following warnings are received on startup:

[20:37:30] [main/WARN]: Found FMLCorePluginContainsFMLMod marker in Forgelin-1.5.1.jar. This is not recommended, @Mods should be in a separate jar from the coremod.
[20:37:30] [main/WARN]: The coremod net.shadowfacts.forgelin.preloader.ForgelinPlugin does not have a MCVersion annotation, it may cause issues with this version of Minecraft
[20:37:30] [main/WARN]: The coremod ForgelinPlugin (net.shadowfacts.forgelin.preloader.ForgelinPlugin) is not signed!

The one about MCVersion is actually quite old. The other two are new to 1.12, and while they don't cause any problems now, the Forge devs plan changes that will break this mod in the future unless they're taken care of.