Implement meta-logging to capture changes at each solve step

[sdboyer]

Tracking lots of individual log message outputs is useful (though still tricky) for development and debugging purposes, but it's mostly useless for end users. One approach to making the output more intelligible would be to create a summary of the state of the solver at each major step in the solve loop, and potentially computing some kind of delta between these states.

[sdboyer]

Actually...once again, pub provides a great guide. Verbose/trace solver logging should look like this.

MAYBE we have a version for debugging specifically...but if the trace is well done, it's probably unnecessary.

[sdboyer]

Got the basics together, so calling this one good enough for MVP.