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7.3 - Changes in the API

• The luaopen_* functions (to open libraries)
  cannot be called directly,
  like a regular C function.
  They must be called through Lua,
  like a Lua function.
• Function lua_open was replaced by lua_newstate to
  allow the user to set a memory-allocation function.
  You can use luaL_newstate from the standard library to
  create a state with a standard allocation function
  (based on realloc).
• Functions luaL_getn and luaL_setn
  (from the auxiliary library) are deprecated.
  Use lua_objlen instead of luaL_getn
  and nothing instead of luaL_setn.
• Function luaL_openlib was replaced by luaL_register.
• Function luaL_checkudata now throws an error when the given value
  is not a userdata of the expected type.
  (In Lua 5.0 it returned NULL.)