All of our sortable headers will have a class of sortable, and the hover modifier in CSS makes it emulate a hyperlink for users. We also are taking advantage of
the CSS class we mentioned about sorted-asc and sorted-desc so that we can show the user the current column that is sorting the table. I didn't include it but
this would be a good place to put background images of arrows pointing up and down as a further visual cue to the user. Now we move on the JavaScript code and the
complexity of sorting, thankfully made easier with jQuery. The code below belongs in the ready() function we started way back at the beginning. Placing this right
above the end of the function is best.