The codec factory should support two distinct interfaces - negotiating
for a serializer with a client, vs reading or writing data to a storage
form (etcd, disk, etc). Make the EncodeForVersion and DecodeToVersion
methods only take Encoder and Decoder, and slight refactoring elsewhere.
In the storage factory, use a content type to control what serializer to
pick, and use the universal deserializer. This ensures that storage can
read JSON (which might be from older objects) while only writing
protobuf. Add exceptions for those resources that may not be able to
write to protobuf (specifically third party resources, but potentially
others in the future).
Add a recognizer that is capable of sniffing content type from data by
asking each serializer to try to decode - this is for a "universal
decoder/deserializer" which can be used by client logic.
Add codec factory, which provides the core primitives for content type
negotiation. Codec factories depend only on schemes, serializers, and
groupversion pairs.
deads2k