Add support for node kinds (hast, xast)

[wooorm]

hast and xast are a bit much to look at: every element has a name (xast) or tagName (hast). This makes that cleaner.

Instead of:

element[0] [tagName="br"]

You now get:

element<br>[0]

The angle brackets are in part inspired by their use in XML, but also sometimes used by Node’s util.inspect:

<ref *1> {
  a: [ [Circular *1] ],
  b: <ref *2> { inner: [Circular *2], obj: [Circular *1] }
}