add optionsAfterRender binding parameter for the options binding. This works similarly to the afterRender option for foreach, except that the first parameter is the option DOM element, instead of an array of elements. The second parameter is the corresponding array item, or `undefined` for the caption option.
Allow optionsAfterRender callback to apply bindings to option.
Merge pull request #929 from SteveSanderson/382-optionsAfterRender

add optionsAfterRender binding parameter for the options binding