hx-headers attribute

• hx-headers can be on parents with javascript8ms ‣

  this.server.respondWith('POST', '/vars', function(xhr) {
    xhr.requestHeaders.i1.should.equal('test')
    xhr.respond(200, {}, 'Clicked!')
  })
  make('<div hx-headers="javascript:i1:\'test\'"><div id="d1" hx-post="/vars"></div></div>')
  var div = byId('d1')
  div.click()
  this.server.respond()
  div.innerHTML.should.equal('Clicked!')