Fix and enhance some things

[zimuya4153]

Added

• Added packet APIs:
  Packet::sendTo, Packet::sendToClients, Packet::sendToServer,
  Packet / LXL_Packet global aliases @zimuya4153
• Added BinaryStream APIs:
  getReadPointer, setReadPointer, setData, writeBytes, readBytes,
  writeUuid @zimuya4153
• Added server APIs:
  mc.getMotd, mc.getOnlinePlayerNum, mc.getMaxNumPlayers,
  mc.getDimensionId, mc.getDimensionName @zimuya4153
• Added gameplay helpers:
  en.setCustomName, mc.summonMob, mc.loadMob, it.addCount,
  it.removeCount, it.setCount, system.randomUuid @zimuya4153
• Added player state APIs:
  pl.isSwimming, pl.isCrawling @zimuya4153
• Added name access APIs:
  be.setCustomName, be.getCustomName, en.getCustomName,
  it.getDisplayName @zimuya4153
• Added player data API:
  mc.getAllPlayerUuids([isOnlineMode]) for enumerating saved player UUIDs
• Added database API:
  DBSession::backup(path) for backing up SQL sessions
• Added VaillanI18n API for modifying Minecraft vanilla language data
  @zimuya4153 @xianyubb
• Added toSNBT([space[,format]]) to all NBT object types @zimuya4153

Changed

• Improved BinaryStream:
  getData([release]) now returns ByteBuffer, does not clear by default, and
  optionally releases data after reading; createPacket(pktid[,raw]) now
  supports raw packets; scalar read* APIs were added; several numeric
  write* APIs now accept String for BigInt-friendly input
  @zimuya4153
• Improved file and item behavior:
  File.readFrom(path[,isBinary]) now supports binary reads;
  File.writeTo(path, text) now accepts ByteBuffer;
  it.setLore([]) now clears custom lore instead of failing @zimuya4153
• Improved player NBT APIs:
  mc.getPlayerNbt(uuid) now returns Null when no saved data exists and can
  read online players directly; mc.setPlayerNbt(uuid, nbt[, forceCreate, isOnlineMode]) now supports optional offline record creation; player NBT
  APIs now validate UUID input more strictly @zimuya4153
• Improved NBT serialization:
  NbtCompound::toSNBT([space[,format]]) now supports explicitly selecting
  SnbtFormat; one-argument usage still defaults to SnbtFormat::ForceQuote
  @zimuya4153

Fixed

• Fixed NbtCompound::setTag @zimuya4153