Possible to cache Gauss-Legendre nodes and weights

[mikeingold]

When integrating using a GaussLegendre rule, we calculate nodes and weights using FastGaussQuadrature.gausslegendre(::Int) -> Tuple{Vector, Vector}.

For geometries that need to be decomposed prior to integration, e.g. Rope -> Segment, the same nodes and weights will be re-calculated for each component of the domain. It might be beneficial, instead, to calculate them once and then pass them through as an optional or keyword argument to _integral.

[mikeingold]

Better idea: store them in the GaussLegendre object itself.