config options for log format and color usage

We want to be able to disable colors for complement logs (since they are likely to be opened in a text editor). There's no pressing need for alternative log formats, but I'm interested in whether the 'pretty' format will be easier for debugging.

I chose to add log_* options rather than making a separate log section for now. There's been some discussion about trying to separate the tracing/logging stuff into more structured sections, but that can happen later.