Break Codec into two general purpose interfaces, Encoder and Decoder,
and move parameter codec responsibilities to ParameterCodec.
Make unversioned types explicit when registering - these types go
through conversion without modification.
Switch to use "__internal" instead of "" to represent the internal
version. Future commits will also add group defaulting (so that "" is
expanded internally into a known group version, and only cleared during
set).
For embedded types like runtime.Object -> runtime.RawExtension, put the
responsibility on the caller of Decode/Encode to handle transformation
into destination serialization. Future commits will expand RawExtension
and Unknown to accept a content encoding as well as bytes.
Make Unknown a bit more powerful and use it to carry unrecognized types.
The pending codec -> conversion split changes the signature of
Encode and Decode to be more complicated. Create a stub helper
with the exact semantics of today and do the simple mechanical
refactor here to reduce the cost of that change.
Make clients opt in to decoding objects that are stored
in the generic api.List object by invoking runtime.DecodeList()
with a set of schemes. Makes it easier to handle unknown
schema objects because decoding is in the control of the code.
Add runtime.Unstructured, which is a simple in memory
representation of an external object.
