optimized and does not put inner-line points in the point set.

      *  mln/accu/accumulators/covariance.hpp: Sumtype/SumSqrType is
         the underlying scalar type, not the sum vector type.
      *  mln/accu/accumulators/cvxhull.hpp: Add missing 'make()'
         generators in cvxhull feature. Optimzation: inner-line points
         are not put in the cvxhull candidate points.