* API: fix faulty pagination behavior
This fix fixes a condition which lead to all messages getting fetched if the limit was a multiple of 100, instead of just the limit.
* API: add NewestMessages
* API: clarify MessageAfter docs
* API: adapt paginating methods for guild, member and message reaction to match the style of message's pagination methods
* API: return nil if no items were fetched
* API: remove Messages and Rename NewestMessages to Messages