fix doc warnings spotted by doxygen 1.8.11

Tested locally

Barycentric_coordinates_2/doc/Barycentric_coordinates_2/Barycentric_coordinates_2.txt

@@ -81,7 +81,6 @@ Example's point pattern.
 
 This is an advanced example that shows how to use generalized barycentric coordinates for height interpolation with applications to terrain modelling. It also shows how to use a non-default traits class with our package instead of a `Kernel` traits class. Suppose we know the boundary of three-dimensional piece of terrain that can be represented as a polygon with several three-dimensional vertices, where the third dimension gives the corresponding height. The task is to propagate the height from the known sample points on the boundary to the polygon's interior. This gives an approximate estimation of the terrain's surface in this region.
 
-\anchor terrain_example
 \cgalFigureBegin{terrain__example,terrain.png}
 A 2D polygon with 50 vertices representing a piece of terrain with convex and concave parts. The height is not shown.
 \cgalFigureEnd
@@ -92,7 +91,6 @@ In this example we project a three-dimensional polygon orthogonally onto the two
 
 As a result we get a smooth function inside the polygon that approximates the underlying terrain's surface.
 
-\anchor terrain_example
 \cgalFigureBegin{terrain__inter__example,terrain_interpolated.png}
 The interpolated data. The colour bar represents the corresponding height.
 \cgalFigureEnd

Documentation/doc/biblio/cgal_manual.bib

@@ -2638,6 +2638,15 @@ pages = "207--221"
   publisher={IEEE}
 }
 
+@incollection{sieger2011design,
+  title={Design, implementation, and evaluation of the surface\_mesh data structure},
+  author={Sieger, Daniel and Botsch, Mario},
+  booktitle={Proceedings of the 20th international meshing roundtable},
+  pages={533--550},
+  year={2011},
+  publisher={Springer}
+}
+
 % ----------------------------------------------------------------------------
 % END OF BIBFILE
 % ----------------------------------------------------------------------------

Mesh_3/doc/Mesh_3/Mesh_3.txt

@@ -611,11 +611,11 @@ The following code produces a 3D mesh for a domain consisting of several subdoma
 Here, the set of subdomains is given by a vector of vector of signs, whereas the set was built automatically in the previous example.
 Each subdomain corresponds to a sign vector [s1, s2, ..., sn] where si is the sign of the function fi(p) at a point p of the subdomain.
 
-\cgalFigureRef{figuremulti_domain} shows a view of the
+\cgalFigureRef{figuremulti_domain2} shows a view of the
 resulting mesh.
 
 \cgalExample{Mesh_3/mesh_implicit_domains_2.cpp}
-\cgalFigureBegin{figuremulti_domain,multi_domain_2.jpg}
+\cgalFigureBegin{figuremulti_domain2,multi_domain_2.jpg}
 View of a 3D mesh of the relative complement of a torus in a sphere.
 \cgalFigureEnd
 

Point_set_processing_3/doc/Point_set_processing_3/Point_set_processing_3.txt

@@ -378,7 +378,7 @@ It first computes the VCM of the points set using `compute_vcm()`. Then, it esti
 which points belong to a sharp edge by testing if a ratio of eigenvalues
 is greater than a given threshold.
 
-\subsection Point_set_processing_3Example_6 Example
+\subsection Point_set_processing_3Example_10 Example
 
 The following example reads a point set from a file, estimates the
 points that are on sharp edges:

Surface_mesh/doc/Surface_mesh/Surface_mesh.txt

@@ -114,7 +114,7 @@ returning ranges of elements which are compatible with the
 <a href="http://www.boost.org/libs/range/doc/html/index.html">Boost.Range</a>
 library. 
 
-\subsection circulators_example Example
+\subsection iterators_example Example
 
 The following example shows how to obtain the iterator type from 
 a range, alternatives for obtaining the begin and end iterator,
@@ -362,7 +362,7 @@ and when iterating over elements they will not be enumerated in the insertion or
 
 This package is derived from an early version of Daniel Sieger and Mario Botsch package 
 <a href="http://graphics.uni-bielefeld.de/publications/imr11/"><em>%Surface_mesh</em></a>
-\cgalCite{cgal:sb-diesmds-11}, 
+\cgalCite{sieger2011design}, 
 which is inspired from the design of <a href="www.openmesh.org">OpenMesh</a> and the \cgal package 
 \ref PkgPolyhedronSummary.
 

Three/doc/Three/Three.txt

@@ -3,7 +3,6 @@ namespace CGAL {
 
 \mainpage User Manual
 \anchor Chapter_Three
-\anchor chapterThree
 \cgalAutoToc
 \author Laurent Rineau, Sebastien Loriot, Andreas Fabri, Maxime Gimeno
 

Visibility_2/doc/Visibility_2/visibility_2.txt

@@ -54,7 +54,7 @@ Thus, we use the same design used to implement \ref PkgArrangement2Summary point
 Each of the various visibility class templates employs a different 
 algorithm or \em strategy for answering 
 queries\cgalFootnote{The term \em strategy is borrowed from the 
-design-pattern taxonomy~\cite ghjv-dpero-95. 
+design-pattern taxonomy \cgalCite{cgal:ghjv-dpero-95}. 
 A \em strategy provides the means to define a family of algorithms, 
 each implemented by a separate class. All classes that implement the various 
 algorithms are made interchangeable, letting the algorithm in use vary according to the user choice.}.