Allow for non generic type codec

[dolanor]

Right now, codecs work for generic encoding (eg. application/json, text/xml, …)

But in a business app, our types could have their own mime type (eg. application/vnd.mycompany.customers.v1+json).
This would kind mix encoding (json) and structural validation (does customer have the right field in the correct business format?). Some kind of marshal and validate mixup.

I need to think about a way, to mix them without coupling them. I guess the right interface could make wonders.

ref:

• https://restfulapi.net/content-negotiation/#comment-5469
• https://restfulapi.net/content-negotiation/#comment-5153