Context API: support multiple contexts #118
Description
Our global context being assumed as the only context in a program puts several limitations on the project:
- work with parallel contexts: e.g. render both an SVG and a PNG
- switch between contexts: this could be very helpful when working in a REPL - when you want to work on a clean slate, but also don't want to lose the context that you have so far worked on
More than this being an actual use case, I feel that the current API unnecessarily makes these things impossible, given that other than show, all other methods that use the global context are only used internally.