Fixes in covariance and cvxhull accumulators. Cvxhull is now
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.