ENH: Extraction of faces on the caustic surface

This commit adds a new class, Caustics, which implements
functionality for detecting and extracting the faces on
the mesh of the caustic surface from a given tetrahedral
(euler) mesh. A face common to two terahedra with volumes
of opposite sign is an element on the caustic surface
mesh.
ENH: Add caustics param in stream-count utility

Added command-line parameter to the stream-count utility to
indicate whether to compute caustics or not.
ENH: Extraction of faces on the caustic surface

This commit adds a new class, Caustics, which implements
functionality for detecting and extracting the faces on
the mesh of the caustic surface from a given tetrahedral
(euler) mesh. A face common to two terahedra with volumes
of opposite sign is an element on the caustic surface
mesh.

From: George Zagaris <george.zagaris@kitware.com>

git-svn-id: https://svn.alcf.anl.gov/repos/DarkUniverse/hacc/trunk/cosmotools@1914 952bdfbe-fa2e-45c0-a9ae-ac90d4a62daf
ENH: Add caustics param in stream-count utility

Added command-line parameter to the stream-count utility to
indicate whether to compute caustics or not.

From: George Zagaris <george.zagaris@kitware.com>

git-svn-id: https://svn.alcf.anl.gov/repos/DarkUniverse/hacc/trunk/cosmotools@1915 952bdfbe-fa2e-45c0-a9ae-ac90d4a62daf
Merge branch 'svn/trunk'