Add World Events

[TheBrokenRail]

Fixes #3

While this PR is based on the 1.15.2 branch, it used JavaDoc from Yarn 1.16.1.

FabricMC/yarn#1652

[TheBrokenRail]

I have changed the Weft build process so it no longer converts from intermediary -> official, I did this originally for debugging, but I think it makes more sense anyways. Since it is guaranteed for the official mappings to change from 1.16.2-pre1 to 1.16.2-pre2 for instance, while the intermediary mapping will most likely stay the same. It also heavily simplifies the Weft build process. If you would like this change reverted I would be happy to, but IMO converting to official just doesn't make that much sense form what I know.

[Daomephsta]

Don't make multiple unrelated changes in one PR. Each unrelated change should be its own PR.
This applies to any project on any PR-supporting Git host.

With regards to the build process changes, I'm not interested in those. Weft is due to be merged with Yarn, and Warp with Loom.
That'll involve a large rewrite anyway, because the way Warp externally hooks into Loom is a bit of a hack.

[TheBrokenRail]

Might as well close this until Weft is properly merged into Yarn.