Merge RaspberryJuice extensions + tweaks

[tromer]

There are versions of mcpi floating around that adds functionality supported RaspberryJuice:

    Updated to included additional functionality provided by RaspberryJuice:
    - getBlocks() : implemented
    - .create() : can now accept "name" (player name) for use in multiplayer
    - CmdPositioner.getDirection
    - CmdPositioner.getPitch
    - CmdPositioner.getRotation
    - getPlayerEntityId
    - CmdEvents.pollChatPosts

I don't where where that originates and don't see it cleanly maintainted anywhere, but it has made its way into several projects on GitHub:

• https://github.com/wensheng/JuicyRaspberryPie/tree/master/java/mcpi
• https://github.com/teachthenet/TeachCraft-Challenges/tree/master/mcpi
• https://github.com/CoderDojoTC/python-minecraft/tree/master/mcpi

Those versions also made some other tweaks -- and they need careful diffs, as they're not identical.

I suggest merging in those enhancements, with some informative error message in case the server doesn't support the RaspberryJuice extensions.

[tromer]

There's yet another version in the following repo, which is a (messily-done) fork of this repo:
https://github.com/Blockguy24/mcpi-multiplayer-api