Add Rigol DS2000A/MSO2000A Driver

[Tobias-1000]

The commands seem to be similar to the existing "DS" protocol.

I updated the scope detection and did a quick test, but it gets stuck with "Socket read failed (errno=0)".
I will do further testing to find the failing command.

This document contains all supported commands and how to use them:
https://www.batronix.com/files/Rigol/Oszilloskope/_DS&MSO2000A/MSO2000A_DS2000A_ProgrammingGuide_EN.pdf

[Tobias-1000]

The protocol for the DS2000A has minor differences to the DS1000.

I will add a new protocol, where most commands are equal to the existing "DS" protocol and implement the rest.