[NGeneral] Fix #135
[NCuboid] Added PVP entrance/exit message. Added PVP_HIDE flag to hide it. Adds #94
[NCuboid] Add some tests to be sure to add Flags correctly in the future.
[NTalk] Rework /nick command so that it doesn't suck. Fix #129
* Check that provided username is correct
* Limit nicknames to something that, without colors, would be acceptable as a Minecraft username