Performance

- Made Table::optimize a public method.
- Table::optimize called only from handleReportGHistory, where it's
  needed.
- Retaining benchmark.txt, to allow further improvements.

src/report.cpp

@@ -1205,7 +1205,11 @@ std::string handleReportGHistory (TDB& tdb, T& task, Config& conf)
   else
     out << "No tasks." << std::endl;
 
-  return out.str ();
+  // Eliminate redundant color codes.
+  std::string optimized = out.str ();
+  table.optimize (optimized);
+
+  return optimized;
 }
 
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