title: How to bind rx_tap (UIButton) to ViewModel?
body: <p>I have authorization controller with 2 UITextField properties and 1 UIButton. I want to bind my View to ViewModel but don't know how to to do it. 
  This is my AuthorizatioVC.swift:</p>
  
  <pre><code>class AuthorizationViewController: UIViewController {
  
  let disposeBag = DisposeBag()
  
  @IBOutlet weak var passwordTxtField: UITextField!
  @IBOutlet weak var loginTxtField: UITextField!
  
  @IBOutlet weak var button: UIButton!
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      addBindsToViewModel()
  
  }
  
  func addBindsToViewModel(){
      let authModel = AuthorizationViewModel(authClient: AuthClient())
  
      authModel.login.asObservable().bindTo(passwordTxtField.rx_text).addDisposableTo(self.disposeBag)
      authModel.password.asObservable().bindTo(loginTxtField.rx_text).addDisposableTo(self.disposeBag)
    //HOW TO BIND button.rx_tap here?
  
  }
  
  }
  </code></pre>
  
  <p>And this is my AuthorizationViewModel.swift:</p>
  
  <pre><code>final class AuthorizationViewModel{
  
  
  private let disposeBag = DisposeBag()
  
  //input
  //HOW TO DEFINE THE PROPERTY WHICH WILL BE BINDED TO RX_TAP FROM THE BUTTON IN VIEW???
  let authEvent = ???
  let login = Variable&lt;String&gt;("")
  let password = Variable&lt;String&gt;("")
  
  //output
  private let authModel: Observable&lt;Auth&gt;
  
  init(authClient: AuthClient){
  
     let authModel = authEvent.asObservable()
              .flatMap({ (v) -&gt; Observable&lt;Auth&gt; in
                      return authClient.authObservable(String(self.login.value), mergedHash: String(self.password.value))
                          .map({ (authResponse) -&gt; Auth in
                              return self.convertAuthResponseToAuthModel(authResponse)
                          })
                })
  }
  
  
  func convertAuthResponseToAuthModel(authResponse: AuthResponse) -&gt; Auth{
      var authModel = Auth()
      authModel.token = authResponse.token
      return authModel
  }
  }
  </code></pre>