Fix plurals in a number of manuals

Documentation/doc/Documentation/Developer_manual/cmakelist_script.txt

@@ -31,7 +31,7 @@ linked. Valid options are, for instance, "filesystem" or "program_options".
 
 </DL>
 
-This options should suffice to create `CMakeLists.txt` script
+These options should suffice to create a `CMakeLists.txt` script
 for most directories containing programs. However, in some special
 cases, it might still be required to create the script manually, for
 instance, if some source files/executables need a different linking than

Mesh_3/doc/Mesh_3/Mesh_3.txt

@@ -422,7 +422,7 @@ Specifically, it is
 either a constant or a spatially variable scalar field. It
 provides an upper bound for the distance between the circumcenter
 of a surface facet and the center of a surface Delaunay ball of this facet.
-<LI><I>`facet_topology`.</I> This parameters controls the set of topological constraints
+<LI><I>`facet_topology`.</I> This parameter controls the set of topological constraints
 which have to be verified by each surface facet. By default, each vertex of a surface
 facet has to be located on a surface patch, on a curve, or on a corner. It can
 also be set to check whether the three vertices of a surface facet belongs to the same

Periodic_3_mesh_3/doc/Periodic_3_mesh_3/Periodic_3_mesh_3.txt

@@ -375,7 +375,7 @@ Specifically, it is
 either a constant or a spatially variable scalar field. It
 provides an upper bound for the distance between the circumcenter
 of a surface facet and the center of a surface Delaunay ball of this facet.
-<LI><I>`facet_topology`.</I> This parameters controls the set of topological constraints
+<LI><I>`facet_topology`.</I> This parameter controls the set of topological constraints
 which have to be verified by each surface facet. By default, each vertex of a surface
 facet has to be located on a surface patch, on a curve, or on a corner. It can
 also be set to check whether the three vertices of a surface facet belongs to the same

Polygon_mesh_processing/doc/Polygon_mesh_processing/Polygon_mesh_processing.txt

@@ -569,7 +569,7 @@ The following running times were observed:
 ***************************************
 \section PMPPredicates Predicates
 
-This packages provides several predicates to be evaluated with respect to a triangle mesh.
+This package provides several predicates to be evaluated with respect to a triangle mesh.
 
 \subsection PMPDoIntersect Intersections Detection
 Intersection tests between triangle meshes and/or polylines can be done using

Polyhedron/doc/Polyhedron/Polyhedron.txt

@@ -111,7 +111,7 @@ are provided too.
 The example continues with a test if the halfedge
 actually refers to a tetrahedron. This test checks the connected
 component referred to by the halfedge `h` and not the polyhedral
-surface as a whole. This examples works only on the combinatorial
+surface as a whole. This example works only on the combinatorial
 level of a polyhedral surface. The next example adds the geometry.
 
 \cgalExample{Polyhedron/polyhedron_prog_simple.cpp}

TDS_2/doc/TDS_2/TDS_2.txt

@@ -72,7 +72,7 @@ the set of maintained faces
 is topologically
 equivalent to a two-dimensional triangulated sphere.
 
-This rules extends to lower dimensional triangulation data structure
+This rule extends to lower dimensional triangulation data structure
 arising in degenerate cases or when the triangulations
 have fewer than three vertices.
 A one dimensional triangulation structure maintains a set of vertices

Triangulation_on_sphere_2/doc/Triangulation_on_sphere_2/Triangulation_on_sphere_2.txt

@@ -143,7 +143,7 @@ Two traits classes are offered with this package as models of the concept `Delau
       for points on the sphere: given a point `p` in 3D space, this traits class manipulates directly
       its projection on the sphere (that is, the intersection of the sphere and the segment with endpoints
       `p` and the center of the sphere). Consequently, all points to be inserted are on the sphere.
-      This traits enable manipulating points that are not on the sphere, but whose triangulation
+      This traits class enables manipulating points that are not on the sphere, but whose triangulation
       on the sphere is still interesting, such as geographical coordinates with altitude.
   </li>
 </ul>