Improving handler debugging UX

This has come up on the message list a few times.  This is more of a concept than a real PR ATM.  The idea is to catch handlers run with no STDIN, and print out a message pointing them to the doc page for debugging handlers.

I'm operating under the assumption that we don't want to change the Utils methods so this change to `read_event` is backwards compatible with IO object (even though I think it is only called with STDIN, at least in this codebase)

Thoughts?