Macro beaker::context

macro_rules! context {
    ($ctx:ident, config={ $key:ident: $cfg:ident }) => { ... };
    ($ctx:ident, config={ $key:ident: $cfg:ident }, config_file=$cfg_file:expr) => { ... };
    ($($ctx:ident, config={ $key:ident: $cfg:ident });+) => { ... };
    (config_file=$cfg_file:expr; $($ctx:ident, config={ $key:ident: $cfg:ident });+) => { ... };
}