Fixed zone allocating functions always throw std::bad_alloc() if allocation is failed.
Added EXT support.
Removed obsolete unpack functions.
Updated examples that no longer use obsolete functions.
Added reference checking function to unpacked. ( unpacked::referenced() )
Added std:: namespace.
Added reference or copy choice function and default behavior:
  When you use unpacker, default behavior is:
    STR, BIN, EXT types are always held by reference.
  When you don't use unpacker, default behavior is:
    STR, BIN, EXT types are always held by copy.
    The memory is allocated from zone.
  You can customize the behavior passing your custom judging function to unpack() or unpacker's constructor.