Macro ecs::systems

macro_rules! systems {
    {
            $(#[$attr:meta])*
            struct $Name:ident<$components:ty, $services:ty>;
        } => { ... };
    {
            $(#[$attr:meta])*
            struct $Name:ident<$components:ty, $services:ty> {
                active: {
                    $($field_name:ident : $field_ty:ty = $field_init:expr,)*
                },
                passive: {
                    $($p_field_name:ident : $p_field_ty:ty = $p_field_init:expr,)*
                }
            }
        } => { ... };
}