A rust prodedural macro that creates UTF-16 encoded literals (as `&[u16; N]`)

```rust
#[macro_use]
extern crate utf16_literal;

extern "system" {
    fn MessageBoxW(*const (), *const u16, *const u16)
}

fn main() {
    let title = u16!("Rust Code\0");
    let msg = u16!("Hello World\0");
    unsafe {
        MessageBoxW(::std::ptr::null(), msg, title, 0);
    }
}
```