[Enhancement] Expose method to bind to additional elements

[Craga89]

We can add a newly exposed method to support the use case of handling events within <iframe> and similar elements that don't bubble their events? Such as:

// Exposed on the `Mousetrap` object
bindEvents: function(el) {
    _addEvent(el, 'keypress', _handleKeyEvent);
    _addEvent(el, 'keydown', _handleKeyEvent);
    _addEvent(el, 'keyup', _handleKeyEvent);
}

// Proxy events from our <iframe> element to Mousetrap
var iframeDocument = document.querySelector('iframe').contentDocument;
Moustrap.bind( iframeDocument );

See #107

[mightyiam]

My fork, https://www.npmjs.org/package/combokeys, has this feature:

var combokeys = new Combokeys(document.getElementById("someIframeOrSomething"));

And then your combokeys instance is bound to that element.

[rtorcato]

mighty lam can your comborkeys package be used without requirejs?

[mightyiam]

@rtorcato you can use Browserify to make a UMD out of it, with Browserify's --standalone option.

[rtorcato]

ok thanks