[geometries][doc] Improve the description of constructors of non-complex geometries.

Add missing descriptions.
Unify the non-initializing default constructors descriptions.

doc/doxy/Doxyfile

@@ -89,6 +89,7 @@ ALIASES                = qbk{1}="\xmlonly <qbk>\1</qbk> \endxmlonly" \
 			param_x="First coordinate (usually x-coordinate)" \
 			param_y="Second coordinate (usually y-coordinate)" \
 			param_z="Third coordinate (usually z-coordinate)" \
+                        constructor_default_no_init="Default constructor, no initialization" \
 			constructor_default{1}="Default constructor, creating an empty \1" \
 			constructor_begin_end{1}="Constructor with begin and end,  filling the \1" \
 			constructor_initializer_list{1}="Constructor taking std::initializer_list, filling the \1" \

include/boost/geometry/geometries/box.hpp

@@ -50,6 +50,7 @@ class box
 
 public:
 
+    /// \constructor_default_no_init
     inline box() {}
 
     /*!

include/boost/geometry/geometries/point.hpp

@@ -108,7 +108,7 @@ private:
 
 public:
 
-    /// @brief Default constructor, no initialization
+    /// \constructor_default_no_init
     inline point()
     {
         BOOST_STATIC_ASSERT(DimensionCount >= 1);

include/boost/geometry/geometries/point_xy.hpp

@@ -45,7 +45,7 @@ class point_xy : public model::point<CoordinateType, 2, CoordinateSystem>
 {
 public:
 
-    /// Default constructor, does not initialize anything
+    /// \constructor_default_no_init
     inline point_xy()
         : model::point<CoordinateType, 2, CoordinateSystem>()
     {}

include/boost/geometry/geometries/segment.hpp

@@ -40,9 +40,13 @@ template<typename Point>
 class segment : public std::pair<Point, Point>
 {
 public :
+    /// \constructor_default_no_init
     inline segment()
     {}
 
+    /*!
+        \brief Constructor taking the first and the second point
+    */
     inline segment(Point const& p1, Point const& p2)
     {
         this->first = p1;
@@ -83,6 +87,9 @@ public:
     point_type& first;
     point_type& second;
 
+    /*!
+        \brief Constructor taking the first and the second point
+    */
     inline referring_segment(point_type& p1, point_type& p2)
         : first(p1)
         , second(p2)