hx-boost attribute

• handles basic form post with button formaction properly9ms ‣

  this.server.respondWith('POST', '/test', 'Boosted')
  var div = make('<div hx-target="this" hx-boost="true"><form id="f1" method="post"><button id="b1" formaction="/test">Submit</button></form></div>')
  var btn = byId('b1')
  btn.click()
  this.server.respond()
  div.innerHTML.should.equal('Boosted')