The select boxes wouldn't always get populated asynchronously in time
for timetasker to make its selections. Increase the timeout to give it a
little more headroom.

Include information about recent changes.

The checkbox wasn't getting filled in correctly. By some overzealous and
uncaught copy-pasting, I had wrapped the field in the function to
populate a select box. Since this is a checkbox, we want to use its
`.checked` property instead.

Use a timeout also. By default Time Task marks Billable as true/checked.
If the script unchecks the box and then the AJAX select box population
occurs, the check box re-checks itself. Adding a timeout allows it to
remain unchecked if you've set that in the user options.

Make it a little clearer what's going on in the date picker event
handler.

Include some background information about the extension, installation
instructions, and release information.