Added OidSet, almost complete, except OidSet.toString()
Modify Oid indicate only one object
Throw exception when Oid class name is invalid
Merge branch 'oid' into oidset
Modify OidSet test case for Oid indicate only one object
Remove OidSet each return
Remove Set.each() return value, and modify it function argument format
Modify Set.equals() to compare set.elements
Modify OidSet.each() function argument format
Let Set support more data type