Using cat relies on coreutils (or equivalent) being in $PATH, which is
not always true.
We could write ${pkgs.coreutils}/bin/cat but in this case we can get by
with the 'read' builtin
While here, cleanup a bit to avoid the x/bin/x patterns we can easily
avoid:
- use lib.getExe for anki-sync-server
- use writeShellScript instead of writeShellScriptBin
Provide a NixOS module for the [built-in Anki Sync
Server](https://docs.ankiweb.net/sync-server.html) included in recent
versions of Anki. This supersedes the `ankisyncd` module, but we should
keep that for now because `ankisyncd` supports older versions of Anki
clients than this module.
