Clojurians Log v2

I episodically get frustrated waiting for new babashka releases announced here to propagate through nixpkgs approval, so had the robot write a flake with an overlay with packages for the latest release (`pkgs.babashka`) and the latest commit (`pkgs.babashka-snapshot`). It's just wrapping the CI-built binaries from the babashka repo, and should pick up new releases with a <= 6 hour lag. See https://github.com/cormacc/nix-babashka if it's of any use to anyone else.