Change "definicoes.h" and "matematica.c"

Change struct to store f(x,y).
Program instead of calculate f(x,y) in each iteration, it just store
f(x,y) in the function create "Grade" and later in the iteration
just read value in the struct.
Add "inline" to all functions.

Signed-off-by: Gustavo Toshi Komura <gtk10@c3sl.ufpr.br>