message: Improved the changelog.
diff: Development version, not released yet
  =====================================
  -- Memory optimizations in the NCMesh class, which now uses 50% less memory in
  - total. The average cost of an NC element (including the refinement hierarchy,
  - but not including the temporary face_list and edge_list) is now only about 290
  - bytes, resulting e.g. in 30-40% timing improvement in ex1.
  +- Memory optimizations in the NCMesh class, which now uses 50% less memory.
  + The average cost of an NC element in a uniformly refined mesh (including the
  + refinement hierarchy, but excluding the temporary face_list and edge_list)
  + is now only about 290 bytes. This also makes the class faster.
  Version 3.3, released on Jan 28, 2017
  