Proposal - change takesElementScreenshot to use takeScreenshot with a parameter

I would like to propose that 16.3 use the same method as in 16.2 and 
that 16.2 take an additional parameter of the element ID.

e.g.
Command Name 	takesScreenshot
Parameters 	"sessionId" {string} The key that identifies which session 
this request is for.
"elementId" {string} The key that identifies which WebElement must be 
captured
Return Value 	{string} A Base64 encoded, lossless PNG of the current 
window.
Errors 	WebDriverException if the screenshot cannot be taken.



This will simplify code for the remote end and will just be an extension 
to the current URL in the JSON Wire Protocol to 
//session/:sessionId/screenshot/:id/

David