0.6

0.6 2018-05-29

• Add a parameter version to Dblib.connect to be able to choose
  the protocol version. Explain how the old protocol versions
  do not allow empty strings which will be returned as ' '.
• Keep the compatibility with FreeTDS version < 0.91.
• Keep int64 as such on the OCaml side (they used to be transformed
  into strings).
• Document Dblib.severity.
• Make error messages more informative by splicing the binding on a
  finer level. A configure script ensures the synchronization with
  values defined in the C header files.
• Add tests for Dblib and Ct (checked by AppVeyor on
  Windows/mingw).
• Improve the interface of Ct.get_messages.
• Complete the depexts list.