[contribution] Working on long-missing feature transcoders;

[Timo Sulg]

Hi,

i started working on long missing feature - transcoders;
Before i'll bundle my changes to pull-request, i'll have a few questions:

• where to put Nippy custom-transcoder i added to compare it with default serializer?
  I think best place would be documentation, that helps to keep number of dependencies low
• Are multimethods fine for initializing Transcoder instances? Or is there better pattern for this?

changes: master...timgluz:add_transcoder