add some other quadrature methods

[chillenb]

This code is very experimental and could have subtle mistakes. Use with caution. (probably create a new branch to play with it)

Often, trapezoidal quadrature is already superior to Gregory (and repeated Simpson) for small k, but very high order Gregory quadrature can beat it.

Enjoy!!

[chillenb]

The Gregory quadrature method in this code is the one described in https://doi.org/10.1016/j.cpc.2020.107484.

It seems to be the same method as Appendix I and II of https://doi.org/10.1093/imanum/2.2.131 This paper is a very good reference.