Macro rucky::import_crates

macro_rules! import_crates {
    ( ) => { ... };
    ( $krate:ident ; $( $rest:tt )* ) => { ... };
    ( $($krate:ident),+ ; $( $rest:tt )* ) => { ... };
    ( $(#[$attr:meta])+ $($krate:ident),+ ; $( $rest:tt )* ) => { ... };
    ( $( $krate:ident ),* / $attrs:tt ) => { ... };
    ( $krate:ident ( $($attr:meta),* ) ) => { ... };
}

Macro to generate extern crate statement at once.