multihash encoding of Digests.

Example:

>>> :set -XOverloadedStrings
>>> import qualified Crypto.Hash as C
>>> import Data.ByteArray.Encoding (Base(..), convertToBase)
>>> import Data.ByteString (ByteString)
>>> import qualified Data.ByteString.Char8 as C8
>>> import System.IO (stdout)
>>> :{
    let
        input :: ByteString
        input = "multihash"
        atBase :: Base -> Multihash -> ByteString
        atBase base = convertToBase base . encodedBytes
     in
        C8.hPutStr stdout $ C8.unlines
            [ atBase Base16 $ multihash C.SHA1   input
            , atBase Base32 $ multihash C.SHA1   input
            , atBase Base16 $ multihash C.SHA256 input
            , atBase Base32 $ multihash C.SHA256 input
            ]
:}
111488c2f11fb2ce392acb5b2986e640211c4690073e
CEKIRQXRD6ZM4OJKZNNSTBXGIAQRYRUQA47A====
12209cbc07c3f991725836a3aa2a581ca2029198aa420b9d99bc0e131d9f3e2cbe47
CIQJZPAHYP4ZC4SYG2R2UKSYDSRAFEMYVJBAXHMZXQHBGHM7HYWL4RY=