Add back support for run length encoding

[mithro]

Run length encoding is important when your sample rate is much higher than your actual rate of change.

The simplest format is that the highest bit indicates if this is a sample or a "repeat the last sample x times" value.

Probably best to follow what the Open Bench Logic Sniffer / SUMP do? More info;

• http://dangerousprototypes.com/docs/Logic_Sniffer_103
• https://sigrok.org/gitweb/?p=libsigrok.git;a=blob;f=src/hardware/openbench-logic-sniffer/protocol.c;h=0d6efeb85a89fd41d2a21dd81ee3aa400e4c664c;hb=HEAD#l389

Adding this issue so I don't forget about it.

[jevinskie]

If the high bit method is used, it could be useful to allow grouping of signals into RLE groups. e.g. one for some usually fast data (or no RLE there at all) and two other RLE groups for control signals for, say, block A and B that are have high activity at different times.