Variant encoding/decoding policy.

[3Hren]

MessagePack has no specification about how to encode variant types. Thus we are free to do whatever we want.

Every Rust variant value can be represented as a tuple of index and a value, and we encode/decode them this way by default, but the given chose may be not ideal for you.

The first solution I've imaging is to introduce enum policies as a template parameter attached to Encoder and Decoder with default value of course.

[seppo0010]

The problem also rises in json. Following rustc-serialize json implementation might be a good option.

[3Hren]

Partially solved for encoding structs, for enums the strategy will be the same.

[3Hren]

Closed with #44.