Dynamically update a clock

In a recent project I had a need to dynamically update a clock, so I added the following methods:

- `setSeedTime` - This method allows the seedTime to be changed dynamically. For example:

    $('.jclock').jclock('setSeedTime', (new Date()).getTime());

- `stopClock` - This method clears the clock's internal timer, stopping the clock. This could also be used in preparation for cleaning up a clock:

    $('.jclock').jclock('stopClock');

- `startClock` - This method will restart a stopped clock:

    $('.jclock').jclock('startClock');

There are also two new example files to demonstrate how to use these new methods.