Better handling of val() on a checkbox.

Before it returned "true" or "false" as a string.  Now it returns the
value of the "value=" attribute if it exists and is checked, the string
"checked" if no "value=" attribute exists and is checked, or "" (an
empty string) if it is not checked.
Simple macro reification cleanup
Better handling of partial placeholders for html.

More issues to do with <span> not going inside a <tr> etc.
Add widget event triggering.

Example usage:

    <input dtx-on-keyup="trace(_.val())" />

The "_" is a shortcut for the currentTarget of the event, or more simple, the current element.
This will call, in your widget's init() function:

    this.[shortcutToInputElement].on(function(e:js.html.Event) {
        trace ( e.currentTarget.val() );
    });

Pretty handy.