#23 Deviation warning, when metric outside normal range.

[Ben Clewett]

Compare the current value of a metric to it's average. If
outside the standard deviation * 2, ie, in the 4% range,
can assume something significant is going on, report to
user.

Need a table specifically for average data, using a
deccaying average over period of a day, every minutes.
Table.

More for perfparse to do, less for CGI to do as this can
be used for a direct average plot rather than clever but
heavey current method.