Fast Player Minecarts

First release.

Minecarts with a player riding them travel 3x faster by default, about 24 blocks per second. Every other minecart keeps vanilla physics, including hopper, chest, furnace, TNT, spawner and command block carts as well as empty and mob ridden ones.

The multiplier can be set from 1 to 8 with /fastcarts multiplier, takes effect immediately and is saved to config/fastcarts/settings.json.