Allow MOAB k-d tree to be configured (#2976)

docs/source/io_formats/statepoint.rst

@@ -96,6 +96,8 @@ The current version of the statepoint file format is 18.1.
               - **library** (*char[]*) -- Mesh library used to represent the
                                           mesh ("moab" or "libmesh").
               - **length_multiplier** (*double*) Scaling factor applied to the mesh.
+              - **options** (*char[]*) -- Special options that control spatial
+                                          search data structures used.
               - **volumes** (*double[]*) -- Volume of each mesh cell.
               - **vertices** (*double[]*) -- x, y, z values of the mesh vertices.
               - **connectivity** (*int[]*) -- Connectivity array for the mesh

docs/source/io_formats/tallies.rst

@@ -364,6 +364,10 @@ attributes/sub-elements:
     The mesh library used to represent an unstructured mesh. This can be either
     "moab" or "libmesh". (For unstructured mesh only.)
 
+  :options:
+    Special options that control spatial search data structures used. (For
+    unstructured mesh using MOAB only)
+
   :filename:
     The name of the mesh file to be loaded at runtime. (For unstructured mesh
     only.)