Allow specifying subset of document

[mischkl]

For using tlite within widgets, it would be nice if we could configure where the event listener is placed. That way we could also ensure that nothing else on the website ends up blocking the event propagation.

[chrisdavies]

That's a good point. I'll accept a PR for this! Right now, I'm pretty swamped w/ other work, so haven't been able to give my various pet projects any love. :/