Extract client code into a plugin

After some discussion with Phil about how we could improve documentation for PureScript libraries, we arrived at a design where we would like to have GitHub Pages-hosted documents easily embed runnable PureScript snippets, with something like script or pre tags, and a plugin that adds a "Run" button, posts the code to the Try PS API when the user clicks, and finally renders the output (below the snippet).

I have not had time to look into how this code is doing stuff right now, just throwing this out there. 😄

Thx!

No files, tests, or entry points are named. Start by mapping the existing client code and its Try PS API integration, then clarify the plugin boundary and embedding approach. Done means GitHub Pages-hosted documents can embed runnable PureScript snippets, offer a Run button, post code to the Try PS API, and render the output below the snippet.