constants/game/difficulty: Update pkg docs.
constants/game/gamemode: Add pkg docs.
material: Add pkg docs.
server: Add pkg docs.
server/player: Add pkg docs.
server/player: Add methods + docs.

- SetX/SetY/SetZ are analogs to SetPos.
- SetPitch/SetYaw are analogs to SetLook.
- Added BroadcastMessage.
server: 0x03 related. Fixes #13.
server: Fix dummy chunk generation. Helps #2.

- Biomes properly set.
- Anvil support almost there!