hx-ext attribute

• Extensions are merged properly12ms ‣

  this.server.respondWith('GET', '/test', 'Clicked!')
  make('<div hx-ext="ext-1"><button id="btn-1" hx-get="/test" hx-ext="ext-2">Click Me!</button>' +
          '<button id="btn-2"  hx-get="/test" hx-ext="ext-3">Click Me!</button></div>')
  var btn1 = byId('btn-1')
  var btn2 = byId('btn-2')
  btn1.click()
  this.server.respond()
  ext1Calls.should.equal(1)
  ext2Calls.should.equal(1)
  ext3Calls.should.equal(0)
  btn2.click()
  this.server.respond()
  ext1Calls.should.equal(2)
  ext2Calls.should.equal(1)
  ext3Calls.should.equal(1)