Add query methods to CMSSummation

[johnynek]

https://github.com/twitter/algebird/blob/develop/algebird-core/src/main/scala/com/twitter/algebird/CountMinSketch.scala#L150

If we had that, we could reuse CMSSummation as a mutable CMS.

[johnynek]

cc @non

[jordanrule]

Am I reading this ticket right in that you just want an accessor/mutator for the private vals in CMSSummation? I'm looking for a good introductory ticket and this could be a good one.

[johnynek]

see:

algebird/algebird-core/src/main/scala/com/twitter/algebird/CountMinSketch.scala

Line 425 in c18a6b7

def frequency(item: K): Approximate[Long]

frequency, innerProduct, totalCount.

The idea is those should also be on the CMSSummation so you don't need to allocate to make queries like that in a mutable context (which is nice to avoid, but not always easy to and retain the highest performance).