JS namespaces (modules) #185

mod features {
    #[node_bindgen]
    pub fn feature_a() -> Result<...> { .... }
}

mod tools {
    #[node_bindgen]
    pub fn tool_a() -> Result<...> { .... }
}

let rustcore = require('rustcore.node');
rustcore.features.feature_a();
rustcore.tools.tool_a();