Clarification of MPFR dependence

[yixuan]

It seems that MPFR is actually optional rather than required if one only wants to use this library to calculate numerical integration instead of generating weights and abscissa (so that only GaussKronrodNodesWeights.h and Integrator.h are used).

Maybe it's better to explain this in README.

[mcsauder]

Hi yixuan,

Thanks so much for the feedback! I've added a few lines to the readme to (hopefully) help clarify when multiprecision is required. Please let me know if you think this helps, and let us know of any other improvements you think can be made as you discover them.

We hope you find the library useful!

-mark

[yixuan]

Thank you for the great work! Just to let you know that I'm using NumericalIntegration in an R package (https://github.com/yixuan/RcppNumerical) of mine. Your library is very helpful. 😄

[cxw42]

Thank you for releasing this library! I am trying it out. I see that CMakeLists.txt still shows MPFR, MPFRCPP, and GMP as REQUIRED. From a few minutes of trying it out, it seems that MPFR is required for the tests, but I can't tell if it is required for the code. Is that indeed the case? If so, should the CMakeLists.txt be updated? Thanks for considering this question!