[common] option: Reformat help and support rST tables

Corners of table have '+' added, and adds new command line flag --rst-help,
which adds some extra formatting to the make it an rST compliant table for the
in-line docs.

common/include/common/option.h

@@ -32,6 +32,13 @@ enum OptionType
   OPTION_TYPE_CUSTOM
 };
 
+enum doHelpMode
+{
+  DOHELP_MODE_NO = 0,
+  DOHELP_MODE_YES,
+  DOHELP_MODE_RST
+};
+
 struct Option;
 
 struct Option