Add measurements

[ltrzesniewski]

From @alprema on February 4, 2016 9:20

There is currently no way to plug easily a metrics system into the Directory without creating a strong dependency, it would be useful to make it plugable so one can monitor Directories efficiently.

The interesting points to measure would be at least :

• Registration time
• Subscription update time
• Total subscription size in MB

Copied from original issue: Abc-Arbitrage/Zebus.Directory#6