Add a rubocop todo-style config created by "--auto-gen-config" and inherit it
Fix an issue reported by rubocop that wasn't ignored in the todo config

Issue text: Favor modifier if/unless usage when you have a single-line body.
Fix several rubocop issues with "rubocop -a"
Fix a few more syntax-related rubocop issues manually
Add brief documentation comments for Homesick and Homesick::Actions
Rename the todo config to .rubocop.yml, now that more rubocop issues are fixed
Add todo comments to the rubocop config