Burndown Chart

- Implemented burndown.daily, which is functional, but has outstanding
  problems that need to be addressed:
    - Slow
    - Does not optimize output (i.e. contains /\S\s+$/)
    - Needs generalized helper functions to reduce the size of the handler

src/Cmd.cpp

@@ -142,6 +142,9 @@ void Cmd::load ()
     commands.push_back ("history.annual");
     commands.push_back ("ghistory.monthly");
     commands.push_back ("ghistory.annual");
+    commands.push_back ("burndown.daily");
+    commands.push_back ("burndown.weekly");
+    commands.push_back ("burndown.monthly");
 
     // Commands whose names are localized.
     commands.push_back (context.stringtable.get (CMD_ADD,         "add"));