add test for NString
fix bugs:
  1. argPos_ has wrong init value
  2. Trim failed to trim right spaces
  3. Replace fall into dead loop when length of src and dst is equal
  4. SubString will fail when startPos exceed data' length
  5. LastIndexOf uses wrong function(find_last_of)
  6. Tokenize work incorrect when szSplliter is empty
  7. ArgImpl forget to increase argPos_