Fix doc for numerical integrations
//! * [Interpolation](numerical/interp/index.html)
//! * [Spline](numerical/spline/index.html)
//! * [Polynomial](structure/polynomial/index.html)
-//! * [Gauss-Legendre Quadrature](special/legendre/fn.gauss_legendre_quadrature.html)
//! * [Lanczos Approximation](special/lanczos/index.html)
+//! * [Numerical Integrations](numerical/integral/index.html)
//! * [Optimization](numerical/optimize/index.html)
//! * Gradient Descent
//! * Levenberg-Marquardt
