0.3.0

API changes

• Added opt-in serde support to facilitate session and ack management (storing subscriptions and
  pids to disk or database). The actual encode()/decode() APIs are unchanged.
• Upgrated bytes dependency to 0.5. This brings growable buffers and a nicer API, amongst other
  things.
• Implemented Default for Pid, From<u16> for Pid, and TryFrom<Pid> for u16. The try_from()
  method already existed but now comes from the std::convert::TryFrom trait.
• encode() now takes anything that implements the BufMut trait, not just a ByteMut struct. For
  technical reasons, decode() still takes BytesMut.
• Added option to opt-out of std library, allowing usage in #[no_std] projects, at the only cost
  of giving up the Error trait from std as well as std::io integration.

Bugfixes

• Fix off-by one error when adding to a Pid wraps over.

Other changes

• The minimum rust version is now 1.39.
• Improved Pid docs.