Update ChewingTextService in order to write string to file immediately

There are some problem before this version.
1.Function getline(buf) via using buf has been not cleared.
  Buf will get gibberish while translating to UTF16.

  This problem is modified now.

2.Write string to defUser.txt immediately instead of writting string after closed Chewing.dll,
  which mean openning both A.notepad and B.notepad and then A.notepad add new string to defuser.txt.
  B.notepad can update buffer immediately