[Idea] Equipment promotions buildings

Inspirated by our equipment promos idea and power up module
http://forums.civfanatics.com/showthread.php?t=380721

I figured out something like this

NOw we have a lot of military productions related buidongs (fleatchers hut, armourer, gunsmith) and their stats are one big mess. Some of them gives +XP (fleatchers hut)
some + % unit production (armourer) and some produce resources (gunsmith).

I think all of them should produce free equipment promotion for units build in that city. Building will also gain XP (when unit is build) to represent that craftsmans in that city achive some kind of mastery in ex bow making so

Fleatchers hut
free fine bow I,II,III promotion for archery units (depending of building xp)

Armourer
free fina armor I,II,III promotion for heavy melee units

Gunsmith
free fine firearms I,II,III promotion for gunpowder

th taht solution we place some kind of order (same stats) for military related building and with power up modcomp creates some kind of city specialization ex best archers in one city, best mele in another.