🏗 Improve JSX block parsing

[johno]

A continuation of #176 that will handle JSX blocks using a custom block parser that extends remark. This will ensure that JSX blocks that contain empty new lines are parsed as a single, cohesive block.

[geddski]

looking forward to this! It will let me have spaces in my code examples

[wooorm]

One thing I’m wondering is whether it would make sense to, as I believe currently JS is embedded in markdown, to swap it around and do markdown in JS.

But I’m guessing what makes the most sense is to remove the html tokeniser and add a custom JSX tokeniser instead (edit: ah, that’s what you’re proposing 🙃)? Something that swallows indented blank lines for example? Or that tracks open and closing tags to find out if the first tag is closed already?