v1.4.2

Use official mojang mappings (#13)

* migrate to official mojang mappings

* remove yarn

* eclipse project + non-null by default

* stuff required to make non-null check happy

* Revert "stuff required to make non-null check happy"

This reverts commit d45d649a9194d1d6ed90be5aff619259c9aef0a6.

* Revert "eclipse project + non-null by default"

This reverts commit 50c2212ba2781ee1b9113d921c0810ee4d38722e.

* update readme instructions

* format