Issues with `import_html.js`

[kentookura]

I will be using the dream-html website quite a lot and expect do run into some edge cases with the markup converter. I'll use this issue to keep track of them.

• got Aria.hidden "true", should be Aria.hidden true
• viewbox takes labelled arguments, but the converter renders a string. In order to handle this, the converter would need to do some parsing.
• got tabindex - 1, should be `tabindex (-1)