Macro combu::default_usage

macro_rules! default_usage {
    ($name:ident) => { ... };
    ($name:ident  as var) => { ... };
    ($name: literal) => { ... };
    ($name:ident : into) => { ... };
    ($name:ident : string) => { ... };
    (nameString=>$name:expr) => { ... };
}

Create usage