New protocol decoder: gpib

Another protocol decoder was recently added to libsigrokdecode: GPIB.

This PD decodes the General Purpose Interface Bus (GPIB, previously also HPIB) protocol, a.k.a. IEEE-488.

This protocol is often used in all kinds of test & measurement equipment, ranging from bench multimeters to power supplies, oscilloscopes and lots more.

We have a few example files in the sigrok-dumps repo, and some test-cases in sigrok-test, as usual.

The decoder was contributed by Rudolf Reuter, thanks a lot!