Number of discovered items.

During low level discovery item collection, send number of mbeans
discovered by low level discovery to detect misconfiguration. Also,
ping item sent will have 0 as a value when exception occured during
item collection for both standard collection and low level discovery
collection.
Also, formatted table in README.md.
Merge pull request #11 from daniel-star/send-ping-and-discovery-status

Number of discovered items.