Changed signs to use TextMessage for storage (fixes #528).

Minecraft 1.8 now stores sign text in json form. When reading signs, lines are
interpreted as plaintext if they fail to parse as json. The API converts from
and to old-style text messages.
Updated readme with forums link.
Validate locations in teleport (fixes #475).
Added basic enchantment definitions (fixes #262).
Minor tidying in GlowEnchantment.
Fixed spectator mode noclip and added game mode event.

Thanks to @coelho for discovering the source of the noclip problem.
Merge pull request #1 from GlowstoneMC/master

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