Additions and tweaks around the date command in particular and ages and dates in general.
- inkarkat/shell-filters for
datediff - automated testing is done with bats - Bash Automated Testing System (https://github.com/bats-core/bats-core)
Download all / some selected extensions (note that some have dependencies, though) and put them somewhere in your PATH, or just add the ./bin subdirectory to PATH.