Topic/reflog reset

`Repository.Reset()` can be added to the list of methods appending to the refolg (as listed there : #389)

Resetting the index do not append a reflog entry; I hope this is the expected behavior.

By the way, I got a bit confused in `Repository` between

    public void Reset(ResetOptions resetOptions, Commit commit)
and

    public void Reset(Commit commit, IEnumerable<string> paths = null, ExplicitPathsOptions explicitPathsOptions = null)

As far as I understood the first signature moves the `HEAD` to the commit, whereas the second one only updates the `Index`. If this is it, I find the naming a bit confusing. Or maybe I missed a subtlety!