Enhancement - #390 timestamps in annotations

- added new dateformat for annotations
- documented prev. added format modifiers H, N and S

src/Config.cpp

@@ -80,6 +80,7 @@ std::string Config::defaults =
   "dateformat=m/d/Y                       # Preferred input and display date format\n"
   "dateformat.holiday=YMD                 # Preferred input date format for holidays\n"
   "dateformat.report=m/d/Y                # Preferred display date format for repors\n"
+  "dateformat.annotation=m/d/Y            # Preferred display date format for repors\n"
   "weekstart=Sunday                       # Sunday or Monday only\n"
   "displayweeknumber=yes                  # Show week numbers on calendar\n"
   "due=7                                  # Task is considered due in 7 days\n"