- reorg `display_alert()` so more frequent levels are handled first
- improve some ANSI color usage, still a mess
- don't write failed commands stackstrace as warnings to screen -- just to file (yes it's redundant, except if in test)
- more useful / subdued stacktraces, to make actual error more obvious...
- do not show path to Docker run-host's logfile, unless the Docker run itself didn't produce logs
- introduce `global_final_exit_code` to allow to maintain/preserve Docker's exit code without triggering an error host-side
- default `SHOW_LOG=yes` if user on terminal
- shortcut: `DEBUG=yes` defaults both `SHOW_LOG=yes` & `SHOW_DEBUG=yes`
- much simpler logging format for log file
- skip all display_alert()'s more verbose than DEBUG from logfile
- set `DEBUG=yes` to log everything again
- skip Markdown assets from being included in ANSI log
- use of `ccze`
- introduce internal var for controlling COMMAND-level log
- remove unused `run_on_sdcard()` that somehow was left there
- drop `export_html_logs()` and `EXPORT_HTML_LOG` -- are no more
