New telemetry packet from cdrDemo

I have updated the telemetry packet sent by cdrDemo.  As often as possible, each pair of floats are now stored in 3 bytes, using a new class called Pair3B.  See the "SAS Network Interface" document on Google Drive.

I will not immediately merge this PR because it will break compatibility with the current GSE build.  Plus, thermvacDemo.cpp will also need to be changed accordingly.