Make CompactMeasurements more useful for DataPublishers

[pixelherodev]

This makes the representation of compactmeasurements lighter, and drops exposed APIs that are only needed internally. It also implements a method for encoding CompactMeasurements into byte buffers for sending across the network.

I tested this with a DataPublisher for PingThings, works well and fast :)

[ritchiecarroll]

How often do you use the compact measurement implementation internally? I had suspected this would be rare as people would generally opt for TSSC mode deployments?

[pixelherodev]

How often do you use the compact measurement implementation internally? I had suspected this would be rare as people would generally opt for TSSC mode deployments?

... exclusively. This is the only mode that our data publisher currently supports.

This wasn't a deliberate choice; someone started working on the data publisher a few years ago and then it got dropped; I just finished it and expanded it, I didn't question their decision of which mode to use.