Discussion: refactor use eventhandler to dispatch events

[keithamus]

When discussing performance concerns with listenForBind() (a discussion motivated by #50), we looked at ways we could optimise the performance of the addEventListener code.

One of the slowest parts of this was creating an anonymous function in a loop. A way around this is to make a centralized event handler which does the heavy lifting. We add some cheap checks inside bindActionsToController - just enough to find out what to bind, then in handleEvent we can do the more detailed checks. This overall looks to work out a bit better (based on my rudimentary benchmarking) for the initial bind than the closure.

The nice thing about this refactoring is it also paves the way for us to listen for mutations on the data-action attribute; we can simply call bindActionsToController if the attribute changes, and it just... works itself out - it avoids double bindings, and unbinding happens automatically because the string check occurs at event dispatch instead of ahead of it.

[keithamus]

Superseded by #53