Schedules need better print methods

[jameslairdsmith]

Schedules are functions. That is a strength of the gs framework. But the default print method R provides for functions aren't informative in this context.

[jameslairdsmith]

A simple set of print methods are provided in #24 , but something more permanent will need to wait for when I have more time. I have sketched out the beginnings of what it will look like in the branch labelled print-methods.