Adding commands so the WattsUp Meter can change between its logging mode...

I made some changes to your code during the 1st year of the EU ASCETiC project
(http://www.ascetic-project.eu/). 

I added code that makes the WattsUp Meter can change its logging mode between: serial,
TCP or internal memory. This helped me use the WattsUp meter and set it into the serial/usb data reporting mode, without this the WattsUp meter I had couldn't be used successfully via the API that you produced.

I also added commands that allows the network configuration to be set for the meters TCP mode.