Minecraft wiki entry for Development_versions, associated text: Villagers now have a daily schedule.
Each villager will try to find their own bed and job site block.
Each profession has a specific block that works as a job site for them (e.g. lectern for the librarian and cauldron for the leatherworker).
A full list of job site blocks and their corresponding villagers below:
Armorer: blast furnace
Butcher: smoker
Cartographer: cartography table
Cleric: brewing stand
Farmer: composter
Fisherman: barrel
Fletcher: fletching table
Leatherworker: cauldron
Librarian: lectern
Mason: stonecutter
Shepherd: loom
Toolsmith: smithing table
Weaponsmith: grindstone
Iron golems will spawn when enough villagers meet.
All villagers will spawn as nitwits (green robes) or unemployed (brown robes) when spawned by spawn egg or commands.
Unemployed villagers have no initial profession, but can change to one by finding a job site block.
Villagers will now show players their trades in their hands if the player is holding certain items which they will trade for.
Mason villagers now have trades.