Macro cached::cached

macro_rules! cached {
    ($cachename:ident >> fn $name:ident ($($arg:ident : $argtype:ty),*) -> $ret:ty = $body:expr) => { ... };
    ($cachename:ident : $cachetype:ident >> fn $name:ident ($($arg:ident : $argtype:ty),*) -> $ret:ty = $body:expr) => { ... };
    ($cachename:ident : $cachetype:ident = $cacheinstance:expr ; >> fn $name:ident ($($arg:ident : $argtype:ty),*) -> $ret:ty = $body:expr) => { ... };
}