Macro aoc_main::run_gen

macro_rules! run_gen {
    ( $day: ident, $data: expr, { gen_default } ) => { ... };
    ( $day: ident, $data: expr, { gen $generator: ident } ) => { ... };
    ( $day: ident, $data: expr, { gen_fallible $generator: ident } ) => { ... };
}