Feature Request: Add support for include_str! macro

[zumoshi]

#[macro_use]
extern crate litcrypt;
use_litcrypt!("FqGaT9DRnfVVoz33j5AaweDT5NoJu7vt");

fn main() {
    println!("{}", lc!(include_str!("../Cargo.toml")));
}

Prints unknown. But I don't see why it shouldn't be possible since the content of the file is known at compile time. The only other crate I found to do what I need was include_crypt which requires the nightly version of rust.