std::bitflags declaration does not allow trailing comma

[chuckries]

From the docs, this works:

bitflags!(
    flags Flags: u32 {
        static FlagA       = 0x00000001,
        static FlagB       = 0x00000010,
        static FlagC       = 0x00000100
    }
)

This would not:

bitflags!(
    flags Flags: u32 {
        static FlagA       = 0x00000001,
        static FlagB       = 0x00000010,
        static FlagC       = 0x00000100,
    }
)

[chuckries]

the macro for vec! does not have this issue.

[aturon]

cc @bjz

[brendanzab]

I agree, this is ugly. I will see if I can fix it.