Send deltas in IoText data protocol - we no need to send always the same values, if they doesn't changed

[bieli]

In this feature request we would like to delivery Schema + versioning in IoText data protocol.

This feature is a must-have for typical telemetric protocol - called deltas.

With the schema versioning technique, we can send only this message with changed values (called deltas):

$|v1,t|3900237526042,d|device_name_001,001=1255,00a=1.566

As you can see, we have special new $ dollar char to show that we send delta values in messages.
In the below example, we use indexes instead of metrics names, but still this is exchanges with metrics names.