Macro utf8 

macro_rules! utf8 {
    ( MIN ) => { ... };
    ( LOW_MAX ) => { ... };
    ( GAP_MIN ) => { ... };
    ( GAP_MAX ) => { ... };
    ( HIGH_MIN ) => { ... };
    ( MAX ) => { ... };
    ( $a:literal ) => { ... };
}

Replaces a few identifiers by their codepoint value, and casts character / integer literals to u32.