Allow chicken-lock output to be redirected with "-output-file" flag
Expose beaker egg via Nix attribute
Allow passing specific paths to chicken-clean
Add flake example to documentation
Add examples of linking to external libraries with Nix helpers
Build egg dependencies in separate step in CI
Update documentation and copyright years
Document the ability to override <nixpkgs> source
Small fixes for Nix helpers and docs
Add "chicken-lock" program