Performance

- Added Timer class to display high resolution timing information.
- Found terrible bug in Table::optimize that was taking up 99.7%,
  on average, of the Table::rendering time, including sorting.  This
  fix naturally causes a 187-fold speedup of rendering.
- Changed report.cpp in handleCustomReport to only load pending tasks,
  instead of all pending tasks.  Subtle, but important difference.

src/report.cpp

@@ -2262,7 +2262,7 @@ std::string handleCustomReport (
 
   // Load all pending tasks.
   std::vector <T> tasks;
-  tdb.allPendingT (tasks);
+  tdb.pendingT (tasks);
   handleRecurrence (tdb, tasks);
 
   // Apply filters.