No need of platform.h

[cvvergara]

Due to the fact that on C++11 isnan & isfinite are part of the standard, there is no need to use platform.h dependency on the build.

tasks:

• change all the upper case that are around the code:
  • ISNAN, IS FINITE to std::isnan std::isfinite respectively
• Some other definitions on platform.h can be change to be constant expressions instead of #define (in constants.h)
• Remove the #define define M_PI 3.14159265358979323846 that are around the code and include the constants.h
• Delete the files platform.h
• Remove references on the build (cmake & autotools) about platform.h

[Paul Ramsey <pramsey@…>]

In a582d47/git:

Using constants.h and stop using platform.h (closes #925)