Support capture events

[josh]

Feature request!

Would ❤️ support for capture events.

on('submit', 'form.js-validate-submission', (event) => {
  // ...
}, {capture: true})

or maybe we're getting kinda long on arguments, support named arguments for the full API:

on({
  event: 'submit',
  selector: 'form.js-validate-submission',
  capture: true
}, (event) => {
  // ...
})

Capture events would run before directly bound event handlers.

on('submit', 'form', (event) => {
  console.log(1)
}, {capture: true})

observe('form', (form) => {
  form.addEventListener('submit', (event) => {
    console.log(2)
  })
})

on('submit', 'form', (event) => {
  console.log(3)
})

Maybe I'll have time to write up a PR, but figured I'd make an issue first.

CC: @dgraham @mislav