[Ur] Access to event object on onclick/et al

[Edward Z. Yang]

Excerpts from Adam Chlipala's message of Sat Jun 23 10:17:39 -0400 2012:
> I'm coming back to thinking about this after a long delay (sorry!).  
> Does anyone know if the event attributes shown below are sufficiently 
> cross-browser to make sense to build into the Ur/Web basis?

Yes, they definitely are cross-browser.  There might be slight behavior
differences but I am not aware of any at the moment.

Edward