Sorting

- Completed sort_compare routine to mimic 1.9.2, but using std::sort.
- Added blank task to the unit tests to prove the sorting is working
  (it wasn't), then fixed all.

src/Table.h

@@ -126,6 +126,8 @@ private:
   std::map <int, just> mJustification;
   std::map <int, bool> mCommify;
   Grid mData;
+
+  // Sorting...
   std::vector <int> mSortColumns;
   std::map <int, order> mSortOrder;