cuekeeper

Merge pull request #45 from alurm/patch-1 make server: remove a buggy dir existance check

Update to newer OCaml versions With `js_of_ocaml` 4.1 and 5.*, it stops updating after a while, so stick to 4.0 for now (probably due to 4.1 adding support for weak refs).

Update build instructions for newer opam

Add flake.nix for Nix users; make server: don't generate keys (to make Nix work) To generate keys, run `nix develop` (optional) followed by `make server/conf/server.pem`.