Add interface definition + stubs for serializer
Add implementation for ws_serializer_json_serializer_new()
Add implementation for serialize() callback
Add key for EVENT
Add interface + stubs for serializer state helper(s)
Add implementation for serializer_context_new()
Add key for the "context" member in the "event" message
Add new state for context member
Add key for event name
Add state for member name
Add state for beeing read with event serializing
Add helper for generating a new key in the buffer
Add implementation for serialize_event()