Adding the ability to configure event listener options, restoring ability to prevent preventDefault() in pointerDown

[tylernotfound]

Follow-up from PR to Unipointer: https://github.com/metafizzy/unipointer/pull/8

Same reasoning around the need for adding listenerOpts applies.

I'm also hoping you reconsider leaving the ability to prevent event.preventDefault() in pointerDown, without actually quitting the event chain via this.okayPointerDown(). The main reason for allowing the event chain to continue without event.preventDefault() is to allow inner elements with 'click' handlers a chance to fire. Prevent default in touchstart stops the chain and prevents these events from firing. The structure I've outlined would make this behavior opt-in, leaving the always preventing behavior the default.

Also included a minor fix in the README, which was referencing an internal property that was removed.