hide "Undocumented" for subparser help on RTD (#385)

* adjust documentation for RTD and display

Now, the parser docstring is used as the help string for a given
subparser. This ensures ReadTheDocs displays a string rather than
“Undocumented”

* readthedocs test

* give a blank string for subparser help if the parser function docstring is null so sphinx-argparse doesn't render "Undocumented"

give a blank string for subparser help if the parser function docstring
is null so sphinx-argparse doesn't render "Undocumented"

util/cmd.py

@@ -156,9 +156,14 @@ def make_parser(commands, description):
         parser = argparse.ArgumentParser(description=description, usage='%(prog)s subcommand', add_help=False)
         parser.add_argument('--help', '-h', action=_HelpAction, help=argparse.SUPPRESS)
         parser.add_argument('--version', '-V', action='version', version=__version__, help=argparse.SUPPRESS)
-        subparsers = parser.add_subparsers(title='subcommands', dest='command')
+        subparsers = parser.add_subparsers(title='subcommands', dest='command', metavar='\033[F') # \033[F moves cursor up
         for cmd_name, cmd_parser in commands:
-            p = subparsers.add_parser(cmd_name)
+            help_str = cmd_parser.__doc__ if cmd_parser.__doc__ and len(cmd_parser.__doc__) else None
+            # give a blank string for help if the parser docstring is null
+            # so sphinx-argparse doesnt't render "Undocumented"
+            if (not help_str) and os.environ.get('READTHEDOCS') or 'sphinx' in sys.modules:
+                help_str = "   "
+            p = subparsers.add_parser(cmd_name, help=help_str)
             cmd_parser(p)
     return parser