* add a physics engine which understands gravity
* add jumper example, jumps whenever you chat
* add `respawn` event which fires when you die or change dimensions
* Block instances have a `boundingBox` property, which is currently either
`solid` or `empty`.
* fix `game` event to fire correctly
* `bot.game.spawnPoint` moved to `bot.spawnPoint`.
* `bot.game.players` moved to `bot.players`.
* `bot.quit` has a default reason of "disconnect.quitting" (thanks Darthfett)