title: BindableProperty notify property changed
body: <p>On a custom <code>ContentView</code> I have created a <code>BindableProperty</code> like this </p>
  
  <pre><code>public static readonly BindableProperty StrokeColorProperty = 
      BindableProperty.Create("StrokeColor", 
                              typeof(Color), 
                              typeof(SignaturePadView), 
                              Color.Black, 
                              BindingMode.TwoWay);
  </code></pre>
  
  <p>But I have to notify on property change, as I have to read the property in a custom Renderer, how can I do this? <br />
  If I set it on the <code>PropertyChanged</code> for <code>BindableProperty</code> it  is a static method, so I can not take it from that way :(</p>