Allow function to be specified as callback

[nathanstitt]

Backbone events could be written inline.

This is useful for for cases where it doesn't quite make
sense to create a method just for them. Such as:

Backbone.View.extend({
    events:{
       'click button': function(){ this.quack(1) }
     }
    quack: function(number_of_times){

    }

    unrelated_method: function(){
       this.quack(3);
    }
})

If the callback was just 'quack', it would be passed the Event object.

It can also be useful for adding events later in the view's lifecycle by calling
this.eventManager.bind() with a function that has closure scope.

My personal use case for it is to setup a listener on the form when it renders:

render: function(){
        var special_value = calculateHash();
        AV.prototype.render();
        this.eventManager.bind("change magic.input", _.partial( this._onFieldChange, special_value, _  ) );
        return this;
}

I prefer to use the eventManager vs setting up EventListeners on the element, since eventManager handles teardown on remove().

[kamilogorek]

@nathanstitt I also added sensible error if no method has been found to fix both AmpersandJS/ampersand-view#38 and AmpersandJS/ampersand-view#37 in one shot.

#2 – your commit included