convert u8 to hex

u8tohex.rs

use std::fmt;
struct ByteBuf<'a>(&'a [u8]);
impl<'a> fmt::LowerHex for ByteBuf<'a> {
    fn fmt(&self, fmtr: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        for byte in self.0 {
            try!(fmtr.write_fmt(format_args!("{:02x}", byte)));
        }
        Ok(())
    }
}