The API's implementations of comment creation/updating for both

top-level comments and replies duplicated a lot of code, which could

easily lead to inconsistencies as we go forward. An upcoming change

required changes in 16 places due to this.
In order to clean this up and keep things maintainable, the existing

create_comment() and update_comment() methods in the base comment

resource have been updated to take more state and return a suitable

payload to the client. A new create_or_update_comment_reply has also

been added to handle the reply side of comment creation. These allow the

subclasses to be responsible only for their own field checking and

object fetching, letting the base class handle all the hard work in a

consistent way.
Documentation has also been fleshed out for these methods.

Unit tests pass.