- if surface is only on a single processor, no point merging occurs
  and the pointsMap is empty.

- the writer nFields() is a separate type of accounting (currently
  only needed by VTK legacy) and is independent of the geometry.

- instead of deciding beforehand if a surface format requires a separate
  geometry file (or if a geometry file should be written if no fields were
  written) now determine afterwards if something was written.

  This improves the overall reliability (consistency) and is more
  convenient for the caller as well.

- previously wrapped raw points/faces with a meshedSurfRef on input,
  but now handle the raw -> meshedSurf logic directly within
  surfaceWriter to avoid holding references to temporaries

  Since the updated meshedSurfRef is now modifiable, it can be used
  directly as a redirection mechanism within surfaceWriter.

- add explicit close() in destructor

- The writers have changed from being a generic state-less set of
  routines to more properly conforming to the normal notion of a writer.
  These changes allow us to combine output fields (eg, in a single
  VTK/vtp file for each timestep).

  Parallel data reduction and any associated bookkeeping is now part
  of the surface writers.
  This improves their re-usability and avoids unnecessary
  and premature data reduction at the sampling stage.

  It is now possible to have different output formats on a per-surface
  basis.

- A new feature of the surface sampling is the ability to "store" the
  sampled surfaces and fields onto a registry for reuse by other
  function objects.

  Additionally, the "store" can be triggered at the execution phase
  as well