The upstream version has been updated, and it has been switched to Yarn.
This makes it simple to build it without the need of our own fork.
We need a small fix for yarn2nix for the time being though. See
<https://github.com/financier-io/financier/pull/5> for details.
With this commit, we add nix flake support. Flakes are evaluated in pure
evaluation mode. The script generate.sh does not work in pure evaluation
mode since it node2nix fetches itself resources from the network. In
order to enable pure evaluation, we add the generated nix files to this
repository.
