Real that uses Fast2Sum for addition I have a feeling this isn't going to improve things at all.

- [D] src/tests/calculatepi.cpp

Ability to define Real as long double `make DEF=-DREAL=2` to compile using long double as Real Also changed calculatepi to include long double. And also, only actually integrate using Real if it is something other than float, double, long double.

- [D] src/tests/calculatepi.cpp

Add tester for numerical calculation of PI Calculate PI using float, double and Real and compare the error and performance. Traditional floats have a point (hardware dependent) where the error starts to behave unpredictably rather than decreasing with number of intervals - due to rounding/precision errors. Can see that doubles are better than single precision floats but they still do it. An infinite precision Real would not have these problems (hah!) We can at least aim to do better than double. Based on PHYS CQM/pprog courses from 2012. Should probably find a literature reference for this.

- [D] src/tests/calculatepi.cpp