Added HASFLAG and experimental DECFLAG

These would be used in the following manner:
enum
{
DECFLAG(VALUE_1) // Is equal to 1
DECFLAG(VALUE_2) // Is equal to 2
DECFLAG(VALUE_3) // Is equal to 4            <---
};
int i = 5;
if (HASFLAG(i, VALUE_1))
std::cout << "Contains i has the VALUE_1 flag";