[ANN] Nimbus: A Nimble-compatible ninja generator

[Anna]

nimbus[0] takes build descriptions written in NimScript and generates
ninja files from them.

Creating this meta-build system allowed me to package all Nitter stack
for Gentoo (see eclass[1] and ebuild[2]).

nimbus is not feature complete yet. For example, it always rebuilds
binaries, even when it's not needed. The sad thing is, upstream doesn't
want to accept my pull request[3] that add depfiles support.

If you are a package maintainer, I hope you find it useful.

[0]: https://git.sysrq.in/nimbus/about/
[1]: https://gitweb.gentoo.org/repo/proj/guru.git/tree/eclass/nimble.eclass?h=dev
[2]: https://gitweb.gentoo.org/repo/proj/guru.git/tree/www-apps/nitter?h=dev
[3]: https://github.com/nim-lang/Nim/pull/19960