title: Posting application/x-www-form-urlencoded using spray
body: <p>I want to "submit a form" through spray like this:</p>
  
  <pre><code>POST / HTTP/1.1
  Host: hoge.org
  Content-Type: application/x-www-form-urlencoded
  
  username=myid&amp;password=mypw
  </code></pre>
  
  <p>I know how to define <code>POST</code>, <code>Host</code> and <code>Content-Type</code>.<br>
  The thing is how to put the contents (<code>username=...</code>) in the request.</p>
  
  <p>Here is my code waiting for the insertion of the contents:</p>
  
  <pre><code>//↑boiler plate↑
  val pipe = (
    addHeader(Host("hoge.org"))
    ~&gt; addHeader(`Content-Type`(`application/x-www-form-urlencoded`))
    ~&gt; sendReceive.apply
  )
  pipe(Post("/")) onComplete {
    case Success(res) =&gt; println("okpk")
    case Failure(exc) =&gt; println(exc)
  }
  </code></pre>
  
  <p>Thank you!</p>