Introduce jackknifeMean and jackknifeVariance functions

These have O(n) cost, vs O(n^2) for jackknife.
Bump version to 0.10.6.0
Add release notes
Switch all vector summation over to KBN
Change Estimator into an algebraic data type

This lets us automatically choose more efficient jackknife
implementations if possible.

--HG--
extra : amend_source : 3c0bf2f7db4ee65ccc2154a304776a06794c72e1
Fix haddock error
Add support for more fast jackknife stats
Merge