Macro typeface::flags

macro_rules! flags {
    ($(#[$attribute:meta])* pub $name:ident($kind:ty) {
        $($value:expr => $variant:ident,)*
    }) => { ... };
    (@base $(#[$attribute:meta])* pub $name:ident($kind:ty) {
        $($value:expr => $variant:ident,)*
    }) => { ... };
    (@read pub $name:ident($kind:ty)) => { ... };
}

Implement flags.