allow setting custom href attribute

I want to be able to set a custom href attribute in the context menu markup that would be more useful than the default "#cmd". This would allow a user to right click a context menu option and choose to open the link in a new tab or window. It also might be useful for a file download option if the user would like to save it to a custom location.
```
$("#mydiv").contextmenu("setEntry", "search", {title: 'go to google', href: 'www.google.com'});
```