* Adds a formatter for nix. Use `nix fmt`.
* Fixes nix standard derivation.
The standard derivation has been broken for quite some time now, but I
didn't use it, so I didn't care to fix it. Today I cared. It now builds
and is updated for the new packaging system.
The older version of `zig-overlay` used was unable to handle the newer
directory layout of Zig tarballs, so `zig-overlay` has been updated and
is currently using a `master` version of Zig.
Additionally, `zls.json` was removed since `zls` will now only look for
it in local or global configuration folders.
Closes#330.
