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

Adding changes made during the 1st year of the EU ASCETiC project
(http://www.ascetic-project.eu/). The changes were made by Richard
Kavanagh (Leeds University).

Adding code so the WattsUp Meter can change between logging to: serial,
TCP or internal memory.
Also adding commands that allows the network configuration to be set for
TCP mode.
Merge pull request #1 from RichardKav/master

Adding commands so the WattsUp Meter can change between its logging mode between: serial, TCP, or internal memory.