Fixes #50 and #51

One static constructor requires the other constructor to finish creating
a cyclic loop. This is easily fixed by removing static constructor for
MetricsConfig and introducing a public static method. This method can be
called from Metric class.

Minimal changes, seems to work for me, but not sure about wider
implications. Please check and accept this pull request if all's good.
Merge remote-tracking branch 'omdr/master' into bugfix/disable-metrics
fix static constructor cyclic dependency. Fixes #50 & #51