Tests for delete counter, contents of folsom counters table are not deleted
Remove counters from folsom counters table on delete operation
Add safe histogram notify functions
Fix histogram of type 'none'

* Before, after filling in the SIZE of the histogram, when adding new values the same element was deleted and updated all the time.
* Tests are included.
Add histogram of type 'slide_sorted'

* This histogram is a simple sliding window of fixed size.
* Tests included.
Merge pull request #1 from Lastres/slide_sorted_esl

Slide sorted esl