Subcommand `lucy compile`

[Arcadi4]

For the ease of testing and just to bootstrap the "install from git" feature, implementing this command can be a good start.

What it does

Simple.

lucy compile https://github.com/dev/modrepo.git -o mod.jar   # full url
lucy compile dev/modrepo -o mod.jar                          # defaults to github

This command:

1. Detects the repo layout (NeoForge? Fabric? gradlew etc.)
2. Checks local toolchain availability
3. Compiles to -o path/to/artifact.jar