Add support for protobuf-serialization 0.2.0.

Does not break support for 0.1.0 thanks to a provided shim.

mvds/Message.nim

@@ -4,14 +4,18 @@ import stew/endians2
 import nimcrypto
 import protobuf_serialization
 
+#Shim until https://github.com/status-im/nim-protobuf-serialization/pull/5 is merged.
+when not defined(protobuf3):
+  template protobuf3() {.pragma.}
+
 type
-  Message* = ref object
+  Message* {.protobuf3.} = ref object
     group* {.fieldNumber: 1.}: seq[byte] #Assigned into a group by developer, not protocol.
     time* {.pint, fieldNumber: 2.}: int64
     body* {.fieldNumber: 3.}: seq[byte]
     id {.dontSerialize.}: seq[byte]
 
-  Payload* = object
+  Payload* {.protobuf3.} = object
     acks* {.fieldNumber: 1.}: seq[seq[byte]]
     offers* {.fieldNumber: 2.}: seq[seq[byte]]
     requests* {.fieldNumber: 3.}: seq[seq[byte]]