Expand functionality of Minecarts

Firstly, I think we need an ability to attach one minecart to another with chain, like we do it with Lead and Mobs, just imagine how much things you can do with it, I'm thinking some kind of "train" when Furnace Minecart makes group of other Minecarts go, however, one Furnace Minecart isn't enough for entire group, so there's choice for player, he can make 1 Furnace Minecart and entire group will go slowly, or he can make more Furnace Minecarts and group will be extremely fast!

But not only that, cause we can attach Chest Minecart and Hopper Minecart and even entire train for Autofarm players.

And yet, I also see one more way to use chains on Minecart - and this is improved roller coaster. Yeah, we already had it, but there were HUGE interval. But with chains, we can turn back at any moment and look in face of our friend.

And finally: A way to use Minecarts with chains is making "Train of Death" with a lot of TNT. Just imagine seeing a train moving forward for you on super sonic speed and with a 1 000 000 of TNT.