Create Event class to use with the serializer.

[marcosschroh]

When encode_record_with_schema_id or encode_record_with_schema is called with data/record, these methods should return an Event object containing the data/record, the payload (the data encoded), the schema_id used to serialize the data and possible kafka_headers rather than the payload encoded.

We want to do this in order to provide more information to the user.

The same should happen with the decode_message. Related to #129

class Event:
    def __init__(self, data, payload, schema_id):
        ...
   
    def headers(self):
       ...

[bboggs-streambit]

@marcosschroh, do you ultimately want to make the return type of serialize and deserialize this Event type? Or should it be configurable?

Is the data the full Kafka message? Or is it just the key or value needing to be serialized or deserialized?
I ask because it sounds like you're envisioning that the headers would be available to pull out of it as a property.