History of GlobalEventHandlers.onerror

Fix invalid call to `alert` with multiple parameters. Improved `alert`'s message readability.

updated explanation of script error handling

scoped function to only catch script errors for special message directing user to browser console

To save developers from researching how to display script errors which is practically impossible.

removed the <img src='x' onerror="alert(JSON.stringify(arguments[0]))"> example, since I'm quite sure the argument will be available simply as |event| in this case. Also clearing the review flags, which were added along with the example.

Format syntax section to be copy-pastable; note the official names of †he arguments, reword the Firefox 31 compatibility note based on markers in the "Syntax" section, and other minor fixups.

Requesting review for my 2 recent changes to Notes section, adding more technical details of arguments passed to inline onerror. Thanks!