Potentially reduce the overheads of scoring each file on every run.
The change also alters the default thresholds for compaction to favour longer runs (which will tend towards greater storage efficiency).
Both log level and forced_logs. Allows for log_level to be changed at startup ad runtime. Also allow for a list of forced logs, so if log_level is set > info, individual info logs can be forced to be seen (such as to see stats logs).
