Pluggable backend

[axelson]

I'm thinking about how to add charts to a scenic-based project and I was thinking that Contex would be a good way to go about it. Do you think a pluggable backend would make sense for contex?

[mindok]

In theory it shouldn’t be too hard - the SVG code is either isolated in a separate module (particularly for the new work) or clearly marked (e.g. function called to_svg). In practice, it would probably be a good idea to do a refactor first, to ensure all drawing functions are properly extracted. It should then be pretty straightforward.