Add JavaScriptCore as new communication mechanism

Hi! In your blog post, you mentioned that communication with a WebView via JavaScriptCore isn't possible. However, there are solutions (see https://github.com/TomSwift/UIWebView-TS_JavaScriptContext) to get access to the JSContext in a UIWebView and then use that to call JS from ObjC and vice versa. I have added a new mechanism using that method. On my iPad, this is about 4 to 5 times faster than the currently fastest method (location.hash, <a> click).