#165: Add bindings for SetZoomLevel in WinForms

> The C++ CEF API exposes the method SetZoomLevel in the CEFBrowser class. Most other methods listed there > already have bindings, but for my project, SetZoomLevel would be very useful.
> http://magpcss.org/ceforum/apidocs/projects/(default)/CefBrowser.html#SetZoomLevel(double)