The plugin system is very rudimentary as of version 0.7.
About the only thing you can do with it is add a column of text to the
output when using -l, -a or -n.

An API will be firmed up for the 0.8 series.

If you make a plugin the name does not matter but it would be nice
if it were prefixed with `yolk-` so its easier to find in the Cheese Shop etc.