Add Stats to KVALRESULTS struct

[ross-spencer]

Have attempted this once but the implementation needs to be better.

• LIS, GET, INS stats are all straightforward to do.
• DEL and REN for keys as well.
• DEL and REN for buckets... less so.
• Once implemented, improve unit tests to make use of the information as well.

Perhaps try a stat() function in the kval-bolt-functions.go functions rather than as a contingency following the successful execution of one of those.

[ross-spencer]

Closed per commits above.