Fix operator precedence

[JoaaoVerona]

Right now, the parser can't really understand the precedence between binary operators.
For example, the sentence println(i == 5 && j == 3) is generating a compile error, because the AND operator (&&) is trying to associate the resultor 'i == 5' with the variable 'j', and not with the resultor 'j == 3'. However, the sentence println(i == 5 && !j) is valid, because there is a unary operator NOT (!) instead of a binary operator.