Make Scales part of formal API and add plot templates #102
Description
A lot of the examples use various "Scale" objects which are defined ad-hoc in the examples, but have a lot of repetition, and people wanting to create standard plots are probably going to want these.
However they are not necessary for things like building UIs or other situations where you are likely to be working in screen coordinates.
This seems like there should be a set of utilities including the scales for creating templated standard plots (line plot, etc.)
Possibly this should just be a completely different library.