This adds SPDX license headers to all source code files, following the
REUSE[1] specification. This does not include any asset files (such as
generated JSON files, or textures). While REUSE does support doing so
with ".license" files, for now we define these licences using the
.reuse/dep5 file.
[1]: https://reuse.software/
This uses pre-commit [1] to check patches are well formed and run
several linters on them. We currently do some boring things (check files
are syntactically valid) as well as some project-specific ones:
- Run illuaminate on the Lua files
- Run checkstyle on Java
[1]: https://pre-commit.com/
More importantly, `./gradlew check' actually runs the in-game tests,
which makes the CI steps look a little more sensible again.
Somewhat depressing that one of the longest files (15th) in CC:T is the
build script.
