Add possibility to generate module for inclusion

[kilork]

This looks like more nice approach, as just directly include generation procedure.

We can achieve a similar thing with the following code:

    let out_dir = env::var("OUT_DIR").unwrap();

    let generated_filename = Path::new(&out_dir).join("generated.rs");
    let generated_rs = "\
mod sets;

pub use sets::generate;";
    std::fs::write(generated_filename, generated_rs).unwrap();

    let generated_dir = Path::new(&out_dir).join("sets");
    std::fs::create_dir_all(&generated_dir).unwrap();
    let mod_filename = generated_dir.join("mod.rs");
    std::fs::write(
        mod_filename,
        "\
mod set_01;
pub use set_01::generate;",
    )
    .unwrap();
    let generated_filename = generated_dir.join("set_01.rs");

    generate_resources(
        "generated",
        None,
        generated_filename,
        "generate",
    )
    .unwrap();

[kilork]

This function should also support multiple sets generation.