Add a serialization mode that mimics outerHTML

[domenic]

That is, it should include the node itself.

Currently in jsdom we have to create a fake parent node with only one child node, the node we want to serialize, and then ask parse5 to serialize that.

[joeldenning]

I've implemented this in #347. For anyone looking for a workaround, here's how you can serialize outerHTML without my new code:

import Serializer from 'parse5/lib/serializer/index.js'

function serializeOuterHTML() {
  const serializer = new Serializer()
  serializer._serializeElement(node)
  return serializer.html
}

[joeldenning]

@fb55 following up from #347 (comment), what would you prefer the name of the new method be? Maybe serializeOuter?

[fb55]

serializeOuter works! We are about to land a major refactor (#362). Once that is done, I look forward to addressing this issue.