The diameter of the drops formed are obtained from the local capillary
length multiplied by the \c dCoeff coefficient which defaults to 3.3.

Reference:
    Lefebvre, A. (1988).
    Atomization and sprays
    (Vol. 1040, No. 2756). CRC press.

surfaceFilmModels::BrunDrippingInjection: New dripping model based on the Rayleigh-Taylor stability analysis
of film flow on an inclined plane by Brun et.al.

    Brun, P. T., Damiano, A., Rieu, P., Balestra, G., & Gallaire, F. (2015).
    Rayleigh-Taylor instability under an inclined plane.
    Physics of Fluids (1994-present), 27(8), 084107.

- separated out the geometry handling into the 'regionModels' library
- regionModels currently includes single layer and 1-D regions
- surface film modelling over-hauled

This reverts commit c5bea524.

This reverts commit b18f6cc1.

- film approximated as single layer mesh, generated using
  extrudeToRegionMesh utility

- library implemented in a hierarchy similar to lagrangian/intermediate:
  - currently includes kinematic and thermodynamic variants

- sub-models include:
  - film detachment/dripping
  - phase change (place holder only)

- works in parallel

- currently in beta status

- handles basic operations, references to other dictionary entries
  (with '$name' syntax) and assorted mathematical functions:

      pi(), degToRad, radToDeg, asin, acos, atan, sin, cos, tan, log,
      log10, mag, atan2, pow

The basic syntax: #calc{ ... };

NOTE the trailing ';' is required for the primitiveEntry to be
properly defined.

- Previously had just 'Warning' instead of '::Foam::Warning', which
  meant that an identically named class method would inadvertently be
  used - resulting in a compile failure.

- needs Coco/R 16 Dec 2009 version

  * added '#remove' function
  * changed insert() method name to more general execute()
  * using #inputMode or #remove within a primitiveEntry now provokes an error
  * adjusted the dictionaryTest accordingly