db::is_exist error,fix it.
singleton v1:demonstrated how singleton work.
value_type of  iterator should as int,show how to check the template argument at compile time.
file_parse:add C style open(), set record number and id number.
bulk_insert:two fields,trouble for static member of class in dll project
create db error
bulk insert for two fields ok,but when debug test,there's exception.
_unlink test.db at first
now debug test could run without exception
import quote data success.