Well, I myself missed the "serialization" part, so it probably was my mistake. Maybe a :note: saying line endings are only added in serialized outputs like the one obtained from `as_string()` or `as_bytes()` but not for other methods that return the body like `get_content()` or `get_payload()` might be helpful.

I stumbled upon it while porting some code from Python 2 to Python 3 and decided to use the new API. But, given the behavior of Python 2's get_content(decode=True), I would say it might just be clearer if docs mentioned this change in behavior (even though the new one is the "correct" one).

I can send in a pull request with modifications if you'd like.