Encoding Unicode strings error

[alanhdu]

When encoding a unicode character, toml seems to accidentally convert unicode hex into decimal:

extern crate toml;
fn main() {
    let s = r#"
         q = "\u000B"
    "#;
    let data: toml::Value = toml::from_str(s).unwrap();
    println!("{:?}", data);
    println!("{}", toml::to_string(&data).unwrap());
}

outputs:

Table({"q": String("\u{b}")})
q = "\u0011"

Found with rust-fuzz/targets#72