"Fix" most warnings when building SpeedCrunch with MSVC

[Tey']

Building SpeedCrunch with MSVC2015 triggers 391 warnings (see attached file). Most of the warnings come from the math library and can be fixed using explicit casts and defining _CRT_SECURE_NO_WARNINGS and _CRT_NONSTDC_NO_WARNINGS. Disabling implicit cast warnings is not a good option.

I'll work on it.