Argument Parsing

- Eliminated stored arg_overrides and file_override in Context.
- Removed Filter, Subst, Task, Sequence from Context.
- Remove shadow file support.  Hallelujah.
- Disabled/commented out most commands, ready for the big transition
  to the new parsing style.
- Obsoleted Subst.{h,cpp}.

src/commands/CmdBurndown.cpp

@@ -982,6 +982,7 @@ int CmdBurndownMonthly::execute (std::string& output)
 {
   int rc = 0;
 
+/*
   // Scan the pending tasks, applying any filter.
   std::vector <Task> tasks;
   context.tdb.lock (context.config.getBoolean ("locking"));
@@ -1017,6 +1018,7 @@ int CmdBurndownMonthly::execute (std::string& output)
 
   chart.scan (tasks);
   output = chart.render ();
+*/
   return rc;
 }
 
@@ -1035,6 +1037,7 @@ int CmdBurndownWeekly::execute (std::string& output)
 {
   int rc = 0;
 
+/*
   // Scan the pending tasks, applying any filter.
   std::vector <Task> tasks;
   context.tdb.lock (context.config.getBoolean ("locking"));
@@ -1070,6 +1073,7 @@ int CmdBurndownWeekly::execute (std::string& output)
 
   chart.scan (tasks);
   output = chart.render ();
+*/
   return rc;
 }
 
@@ -1088,6 +1092,7 @@ int CmdBurndownDaily::execute (std::string& output)
 {
   int rc = 0;
 
+/*
   // Scan the pending tasks, applying any filter.
   std::vector <Task> tasks;
   context.tdb.lock (context.config.getBoolean ("locking"));
@@ -1123,6 +1128,7 @@ int CmdBurndownDaily::execute (std::string& output)
 
   chart.scan (tasks);
   output = chart.render ();
+*/
   return rc;
 }