M_PI does not exist for MSVC

[trevordblack]

MSVC throws errors looking for M_PI

[trevordblack]

https://stackoverflow.com/questions/6563810/m-pi-works-with-math-h-but-not-with-cmath-in-visual-studio

[hollasch]

My vote is to keep it simple. In our constants file (which I think Ronald is working on), we should just use

const <floatType> pi = 3.1415926535897932385;

[ronaldfw]

Fixed on the future branch.

[hollasch]

This should go in to v3 (the development branch).

[hollasch]

Done and now in the development branch.