Implement Encodable for Value
Implement Encodable for Value

We can't generically decode into one, but we can generically encode one!

Closes #58

badboy/toml-rs,vosen/toml-rs,alexcrichton/toml-rs,mseri/toml-rs,GuillaumeGomez/toml-rs,roguePanda/toml-rs,vosen/toml_document,trlim/toml-rs