Two of the new key bindings (default H,Y) use the current selected item in your hotbar, and rotate that column in your inventory up or down.
The other two (default J,U) shift your entire inventory up and down. So each of the three rows of your inventory is an alternate hotbar that you rotate into with one click.
If you link to this page and let me know somehow (comment or twitter @lothrazar), you can use this in a modpack.
Requires Minecraft Forge version 1.8-11.14.3.1446 or higher, from http://files.minecraftforge.net/
Also released for forge-1.7.10-10.13.4.1558
For 1.8.8, use forge 11.15.0.1595 or higher
