* Serialize default values in oneofs when calling to_dict() or to_json()
This change is consistent with the official protobuf implementation. If
a default value is set when using a oneof, and then a message is
translated from message -> JSON -> message, the default value is kept in
tact. Also, if no default value is set, they remain null.
* Some cleanup + testing for nested messages with oneofs
* Cleanup oneof_enum test cases, they should be fixed
This _should_ address:
https://github.com/danielgtaylor/python-betterproto/issues/63
* Include default value oneof fields when serializing to bytes
This will cause oneof fields with default values to explicitly be sent
to clients. Note that does not mean that all fields are serialized and
sent to clients, just those that _could_ be null and are not.
* Remove assignment when populating a sub-message within a proto
Also, move setattr out one indentation level
* Properly transform proto with empty string in oneof to bytes
Also, updated tests to ensure that which_one_of picks up the set field
* Formatting betterproto/__init__.py
* Adding test cases demonstrating equivalent behaviour with google impl
* Removing a temporary file I made locally
* Adding some clarifying comments
* Fixing tests for python38
