0 Compiler warnings (gcc -Wall -Wextra) and PI definition

[acrilique]

Explicit casting was used to get rid of gcc's compiler warnings. Also some variables had their declaration changed from signed to unsigned. M_PI was not defined by my platform's <math.h> so I thought it would be good to have the respective #ifndef #define Although having it in 3 different files isn't really neat, I think it would not make much sense to have another header file just for M_PI.