Function be_uint 

fn be_uint<I, Uint, E: ParseError<I>>(
    bound: usize,
) -> impl Parser<I, Output = Uint, Error = E>
where
    I: Input<Item = u8>,
    Uint: Default + Shl<u8, Output = Uint> + Add<Uint, Output = Uint> + From<u8>,

creates a big endian unsigned integer parser

• bound: the number of bytes that will be read
• Uint: the output type