- prior to sampledSurface supporting different interpolation schemes a
  workaround means was used to simulate cellPoint -> face
  interpolation, with averaging of vertex interpolation.

  We instead now use cellPoint interpolation directly for the face
  values when 'interpolate=true'.

- removes a layer of opacity and may help with future restructuring

- fits better into the general sampling framework, improves flexibilty
  and allows code reduction.

ENH: include surface fields on sampledSurfaces that support it

- 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

- complete any pending initialisation on write().
  Allows lazier evaluation until when the surfaces are actually needed.

Style changes:
    - use lookupObjectRef instead of using const_cast
    - use tmp::New factory

- improvement documentation for surface sampling.

- can now specify alternative sampling scheme for obtaining the
  face values instead of just using the "cell" value. For example,

      sampleScheme    cellPoint;

  This can be useful for cases when the surface is close to a boundary
  cell and there are large gradients in the sampled field.

- distanceSurface now handles non-closed surfaces more robustly.
  Unknown regions (not inside or outside) are marked internally and
  excluded from consideration. This allows use of 'signed' surfaces
  where not previously possible.

- can be useful either for flow-rate weighting where backflow
  is to be ignored in the average, or for flow-rate weighting
  on surfaces with inconsistent orientation.

  Reworked to code to make better use of Enum (the NamedEnum
  replacement). Enum doesn't require contiguous enumeration values,
  which lets us use bitmasking of similar operations to reduce
  duplicate code.

- this makes it possible to perform additional operations
  on surface values that have been previously sampled.

- support vectorField for weighting operations.

- reduce overhead by avoiding creation of weight fields, Sf fields
  and combined surface geometries unless they are actually required.

- extend some similar concepts and operations to volFieldValue

Patch contributed by Timo Niemi, VTT.
Resolves patch request https://bugs.openfoam.org/view.php?id=2452

- currently only 'none' or 'sqrt', which can be useful in combination
  with integrate or averaging functions.

Renamed the original volRegion -> volFieldValue to clarify the purpose
of this class to process vol fields on a volRegion.

functionObjects: Further simplification and rationalization using the fvMeshFunctionObject base-class

functionObjects::surfaceRegion: Write the surface geometry for formats in which the data is in separate files

The use of the term 'source' in the context of post-processing is
confusing and does not properly describe the process of region
selection.  The new names 'surfaceRegion' and 'volRegion' better
describe the purpose of the functionObjects which is to provide field
processing functionality limited to a specified region of space, either
a surface or volume.

The keyword 'source' is renamed 'regionType' which better describes the
purpose which is to specify the method by which the surface or volume
region is selected.

The keyword to select the name of the surface or volume region is
renamed from 'sourceName' to 'name' consistent with the other
name-changes above.

with the more general and flexible 'postProcess' utility and '-postProcess' solver option

Rationale
---------

Both the 'postProcess' utility and '-postProcess' solver option use the
same extensive set of functionObjects available for data-processing
during the run avoiding the substantial code duplication necessary for
the 'foamCalc' and 'postCalc' utilities and simplifying maintenance.
Additionally consistency is guaranteed between solver data processing
and post-processing.

The functionObjects have been substantially re-written and generalized
to simplify development and encourage contribution.

Configuration
-------------

An extensive set of simple functionObject configuration files are
provided in

OpenFOAM-dev/etc/caseDicts/postProcessing

and more will be added in the future.  These can either be copied into
'<case>/system' directory and included into the 'controlDict.functions'
sub-dictionary or included directly from 'etc/caseDict...

regionFunctionObject: moved 'log_' to public 'log' to support the 'Log' macro

  - Avoids the need for the 'OutputFilterFunctionObject' wrapper
  - Time-control for execution and writing is now provided by the
    'timeControlFunctionObject' which instantiates the processing
    'functionObject' and controls its operation.
  - Alternative time-control functionObjects can now be written and
    selected at run-time without the need to compile wrapped version of
    EVERY existing functionObject which would have been required in the
    old structure.
  - The separation of 'execute' and 'write' functions is now formalized in the
    'functionObject' base-class and all derived classes implement the
    two functions.
  - Unnecessary implementations of functions with appropriate defaults
    in the 'functionObject' base-class have been removed reducing
    clutter and simplifying implementation of new functionObjects.
  - The 'coded' 'functionObject' has also been updated, simplified and tested.
  - Further simplification is now possible by creating some general
    intermediate classes derived from 'functionObject'.

functionObjects: Moved into the functionObjects namespace and rationalized and simplified failable construction

Rather than requiring each functionObject to handle failed construction
internally (using the active_ flag) the static member function "viable"
is provided which returns true if construction of the functionObject is
likely to be successful.  Failed construction is then handled by the
wrapper-class which constructs the functionObject,
e.g. "OutputFilterFunctionObject".

Updated objects
- corrected Peclet number for compressible cases
- propagated log flag and resultName across objects

New function objects
- new fluxSummary:
  - calculates positive, negative, absolute and net flux across face
    zones
- new runTimeControl
  - abort the calculation when a user-defined metric is achieved.
    Available options include:
    - average value remains unchanged wrt a given threshold
    - equation initial residual exceeds a threshold - useful to abort
      diverging cases
    - equation max iterations exceeds a threshold - useful to abort
      diverging cases
    - min/max of a function object value
    - min time step exceeds a threshold - useful to abort diverging
      cases
- new valueAverage:
  - average singular values from other function objects, e.g. Cd, Cl and
    Cm from the forceCoeffs function object

Avoids the clutter and maintenance effort associated with providing the
function signature string.

faceSource: Added weightedAreaAverage option
Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1769

This had been used in functionObjects:

    Info(log)<< "messages" << data << ....

in which it is not at all clear what the "log" argument does whereas

    if (log) Info<< "messages" << data << ....

is totally clear and more efficient.