in new package Ocarina.Cmd_Line, rework all
          frontend/backends to avoid code duplication.

          For issue #33

          Also fix for issue #54

          Ocarina.Python_Cmd

          features.

          For issue #56

          Compilation_Time. These requires a recent version of GCC.

        For issue #55

          User's Guide for details.

        For issue #50

        For issue #51

        For issue #50

          supported in regular version of GNAT shipped in Linux

        For issue #50

          routines to fetch various kind of property types.

          First step of #19

          SPARK GPL 2015

          Value_Type

          requirements.