ui: simply concatenate messages before applying color labels This should be cheaper in space than applying labels for each message.

ui: simplify interface of low-level write() functions _write() and _write_err() will be replaced with fout.write() and ferr.write() respectively. This is the first step.

ui: factor out function that writes data to fout/ferr with labeling I'm thinking of adding an option to send status messages to stderr (or a dedicated command-server channel) so that structured output (e.g. JSON) would never be interleaved with non-formatter output. A unified write() interface helps to do that.