Bit fields for Status

[TheoW03]

instead of using raw bits we use this

union
    {
        struct
        {
            unsigned mapper_lower : 4; // lower bits of mapper
            unsigned four_screen : 1;  // if 4 screen
            unsigned trainer : 1;      // trainer. Ie the PRG is a 512 offset
            unsigned battery : 1;      // for zelda (it used a battery to save )
            unsigned vertical : 1;     // if vertical
        };
        byte_t val;
    } flag6;

good readbaility prevents bugs