Dump waves to something better than VCD

## Motivation
VCD files are simple but big and slow. Other formats could be better for disk space and performance.

## Desired solution
Find wave dump format(s) which enable lower space and/or higher performance.

One option could be FST. There's a discussion on adding it to treadle here that may be of interest: https://github.com/chipsalliance/treadle/issues/101

## Alternatives considered
Some vendors and tools have proprietary formats that work well with their debug tools. Perhaps it's worth investigating methods to generate those formats.