inputProp is supported on binding update

The missing functionality of taking a property value of an updated value object was added.

I stuck on the problem that even if I set options.inputProp to some property name, on updating of the binding the whole instance of updated data object was set to HTML Input element's value. Because of this code

        this.update = function (element, valueAccessor) {
            var options = unwrap(valueAccessor()),
                value = unwrap(options && options.value);

            element.value = value;
        };

I updated the logic and now we try to get a property value instead the whole data object value if options.inputProp is set

        this.update = function (element, valueAccessor) {
            var options = unwrap(valueAccessor()),
                value = unwrap(options && options.value),
                props = self.getPropertyNames(valueAccessor);

            element.value = value && props.input ? value[props.input] : value;
        };

Please let me know if it has any problems or I missed something important. Thanks for the great component!