Deprecate defdelegate with lists and append_first

[josevalim]

I believe those features do not map well to Elixir semantics anymore. You want each defdelegate to be on its own line so you can control module attributes like @doc and append_first can be confusing when using defaults (which are more useful than append_first).

/cc @tuvistavie @lexmag

[lexmag]

Strongly 👍 for defdelegate with lists deprecation, not sure about append_first though.

Edit: 👍 for append_first as well.

[danhper]

I totally agree for defdelegate with lists.
I think append_first is useful, but I agree it adds too much complexity compared to the benefits, especially when used with optional parameters.

[josevalim]

@tuvistavie can you please tackle this as well once your PR lands? :)

[danhper]

Sure!