Add error codes to ProtocolError and subclasses
Add error codes to ProtocolError and subclasses

vladmunteanu/hyper-h2,Kriechi/hyper-h2,python-hyper/hyper-h2,python-hyper/hyper-h2,vladmunteanu/hyper-h2,Kriechi/hyper-h2,bhavishyagopesh/hyper-h2