Code.preferred_encoder/decoder should return the objects, not their names

[Johan Rosenkilde]

It makes a lot more sense that C.preferred_encoder() gives me an encoder object, and not the name of an encoder. In almost all uses, otherwise, the user would have to write C.encoder(C.preferred_encoder()).

[David Lucas]

Resolved issue #29

→ <<cset fce530e0a4b1>>