mention alternatives to DateTime.compare/2 for comparison

[roelandvanbatenburg]

During our upgrade to Elixir 1.18 we got some compile warnings about the usage of == on DateTime structs. https://hexdocs.pm/elixir/1.18.1/DateTime.html suggested using compare/2 which led to replacing

  if user.password_reset_token_sent_at > oldest_allowed_token_datetime do

with

  if DateTime.compare(user.password_reset_token_sent_at, oldest_allowed_token_datetime) == :gt do

However, a far better solution is:

  if DateTime.after?(user.password_reset_token_sent_at, oldest_allowed_token_datetime) do

To make it easier for developers to think of these functions (after? and before?), I suggest mentioning them alongside compare/2.

[josevalim]

💚 💙 💜 💛 ❤️

[josevalim]

This may also apply to the docs in Date, Time, and NaiveDateTime. If that's the case, please submit a PR!