Some small convenience things for `emojicode-sys`. 

Example:
```rust
#[macro_use]
extern crate emojicode;

use emojicode::*;

package_version!(0, 1);

emoji_functions!(
    e_hello(thread) {
        thread.return_from_function_with_value(
            String::from("Hello from Rust!")
                .to_value()
                .unwrap()
        );
    }
);

prepare_class!(
    (class, name) {
        println!("{}", name);
    }
);
```