Macro adapton::cell_call

macro_rules! cell_call {
    ( $nm:expr =>> $f:ident :: < $( $ty:ty ),* > , $( $lab:ident : $arg:expr ),* ) => { ... };
    ( $nm:expr =>> $f:ident , $( $lab:ident : $arg:expr ),* ) => { ... };
}

Convenience wrapper: Call a function and place the result into an engine::cell.