After reading about the era of my mod more, and looking back over a few earlier comments, I decided to release a small patch which adds an archer unit to every faction lacking one presently, before this mod goes fully down the memory hole. However, archers are only available at castles, unlike gunners and crossbowmen, to represent the increased difficulty of training them and thus also their comparitive rarity in the period.
List of Units added
Spoiler Alert, click show to read:
Copy over the files contained in the patch into your mod's install folder directory (check the mod's folders if you are unsure, they are likely to be the same). Make a backup of the old files if you're unsure you want to use archers. This version also makes a minor change to start of campaign to (hopefully) prevent the Mamluks from too often winning the short campaign. Use only the "descr_strat" file, or do not use it, if you are interested/not intested in that change only.
EDIT: Forgot to mention, this should be fully savegame compatible and has been tested.
DOWNLOAD LINK FOR (OPTIONAL!) PATCH: http://www.zshare.net/download/83021721652d7855/