v0.5.1: Tags, for `inherit`s

inherit a b; in an attribute set will now also generate tags. It didn't before.

0.5.0: Tags!

This release adds a nix-doc tags subcommand and moves the previous search functionality to nix-doc search.

The new tags feature allows for generating tags files as might be generated by ctags. This allows for efficient editor navigation of nixpkgs and other Nix script projects.