Pluggable architecture #5
Description
Perhaps if we provide an easy-to-maintain pluggable design, others may find it better to extend agio rather than write their own tools. As a start, we could adapt Amir Kamil's tools.
Also, EECS 280 has a single script for downloading the instructor files. We could implement that too.
A good design would be to have plugins live in a sub directory. Each plugin would be loaded automatically as a subcommand.
Also, add an example and link to the example from the Contributing section of the README.