Document upperclass internal constants

[rdlaitila]

We should document the purpose and usage of many of upperclass's internal constants for example:

local UPPERCLASS_SCOPE_PRIVATE = {}
local UPPERCLASS_SCOPE_PROTECTED = {}
local UPPERCLASS_SCOPE_PUBLIC = {}
local UPPERCLASS_SCOPE_NOBODY = {}
local UPPERCLASS_MEMBER_TYPE_PROPERTY = {}
local UPPERCLASS_MEMBER_TYPE_FUNCTION = {}
local UPPERCLASS_TYPE_ANY = {}
local UPPERCLASS_TYPE_STRING = {}
local UPPERCLASS_TYPE_TABLE = {}
local UPPERCLASS_TYPE_FUNCTION = {}
local UPPERCLASS_TYPE_NUMBER = {}
local UPPERCLASS_TYPE_USERDATA = {}
local UPPERCLASS_TYPE_NIL = {}
local UPPERCLASS_TYPE_BOOLEAN = {}