Include error reporting for deserializer

[andrevidela]

The type of deserialiser does not include any error reporting and currently looks like this:

   MkDeserialiser : (Bytes -> Maybe (a, Bytes)) -> Deserialiser a 

We should probably change its type to

   MkDeserialiser : (Bytes -> Either DeserializeError (a, Bytes)) -> Deserialiser a 

with DeserializeError which describe all different ways of failing the deserialization.