crypto/hash: impl Writer for Hasher to allow use of Reader-Writer convenience functions

use libc::c_uint;

use std::ptr;

use std::io;

use ffi;

    len: uint,

}

impl io::Writer for Hasher {

    fn write(&mut self, buf: &[u8]) -> io::IoResult<()> {

        self.update(buf);

        Ok(())

    }

}

impl Hasher {

    pub fn new(ht: HashType) -> Hasher {

        ffi::init();