Added time() function that updates the time

From the documentation: "This command sets the real-time clock by
synchronizing with the time server specified with the time server (set
time) parameters. This command sends a UDP time server request packet."
Added sleep() with wake timer

Added the sleep() command.  Calling it with (seconds) will set the
system wake timer before putting the module to sleep.
Merge pull request #28 from OrganicIrradiation/master

Added time() and sleep() functions