Section about compression

[dsebastien]

Goal: explain how to optimize for compactness

[EmidioStani]

An interesting point would be adding support for binary formats such as Avro or Protobuf

[dsebastien]

@EmidioStani indeed, makes sense.
With the current specs, Avro/Protobuf could also be alternative resource representation formats: https://github.com/NationalBankBelgium/REST-API-Design-Guide/wiki/Data-formats