removed --log-level due to overlap with how --verbose works now.
for consistency, added --info as alias to --verbose (as the effect is
setting INFO log level).
also added --debug which sets DEBUG log level.
note: there are no messages emitted at DEBUG level yet.
WARNING is the default (because we want mostly silent behaviour,
except if something serious happens), so we don't need --warning
as an option.
cb821b119b