Issue53 - Changes to allow 115200 baud rate to be set for USB link.
Handling baudrate preference in a better way.

If this preference does not exist it should default to 57600.
Merge pull request #127 from arthurbenemann/issue53

I haven't tested the code in a device, but I'm sure the modification works. I'm merging it now, if it gives any problem on master we can fix it later.