server: Find better serializer

[simnalamburt]

Currently using json, probably not the best option

[sgkim126]

rust-msgpack is good solution. But there are too many warnings, because it uses too outdated code.
I think we can move to rust-msgpack when the warnings are fixed.

[simnalamburt]

Rust core team is now currenlty working on making Rust's own good object serialization format but not done yet
http://doc.rust-lang.org/nightly/rbml/index.html