added touches documentation

doc/src/examples/algorithms/touches_one_geometry.cpp

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+// Boost.Geometry (aka GGL, Generic Geometry Library)
+// QuickBook Example
+
+// Copyright (c) 2020-2021 Digvijay Janartha, Hamirpur, India.
+
+// Use, modification and distribution is subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+//[touches
+//` Checks if a geometry has at least one touching point (self-tangency)
+
+#include <iostream>
+
+#include <boost/geometry.hpp>
+#include <boost/geometry/geometries/point_xy.hpp>
+#include <boost/geometry/geometries/polygon.hpp>
+
+namespace bg = boost::geometry; /*< Convenient namespace alias >*/
+
+int main()
+{
+    // Checks if the geometry has self-tangency.
+    bg::model::polygon<bg::model::d2::point_xy<double> > poly1;
+    bg::read_wkt("POLYGON((0 0,0 3,2 3,2 2,1 2,1 1,2 1,2 2,3 2,3 0,0 0))", poly1);
+    bool check_touches = bg::touches(poly1);
+    if (check_touches) {
+         std::cout << "Touches: Yes" << std::endl;
+    } else {
+        std::cout << "Touches: No" << std::endl;
+    }
+
+    bg::model::polygon<bg::model::d2::point_xy<double> > poly2;
+    bg::read_wkt("POLYGON((0 0,0 4,4 4,4 0,2 3,0 0))", poly2);
+    check_touches = bg::touches(poly2);
+    if (check_touches) {
+         std::cout << "Touches: Yes" << std::endl;
+    } else {
+        std::cout << "Touches: No" << std::endl;
+    }
+
+    return 0;
+}
+
+//]
+
+
+//[touches_output
+/*`
+Output:
+[pre
+Touches: Yes
+Touches: No
+]
+*/
+//]

doc/src/examples/algorithms/touches_two_geometries.cpp

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+// Boost.Geometry (aka GGL, Generic Geometry Library)
+// QuickBook Example
+
+// Copyright (c) 2020-2021 Digvijay Janartha, Hamirpur, India.
+
+// Use, modification and distribution is subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+//[touches
+//` Checks if two geometries have at least one touching point (tangent - non overlapping)
+
+#include <iostream>
+
+#include <boost/geometry.hpp>
+#include <boost/geometry/geometries/point_xy.hpp>
+#include <boost/geometry/geometries/polygon.hpp>
+
+namespace bg = boost::geometry; /*< Convenient namespace alias >*/
+
+int main()
+{
+    // Checks if the two geometries overlaps or not. 
+    bg::model::polygon<bg::model::d2::point_xy<double> > poly1;
+    bg::read_wkt("POLYGON((0 0,0 4,4 4,4 0,0 0))", poly1);
+    bg::model::polygon<bg::model::d2::point_xy<double> > poly2;
+    bg::read_wkt("POLYGON((0 0,0 -4,-4 -4,-4 0,0 0))", poly2);
+    bool check_touches = bg::touches(poly1, poly2);
+    if (check_touches) {
+         std::cout << "Touches: Yes" << std::endl;
+    } else {
+        std::cout << "Touches: No" << std::endl;
+    }
+
+    bg::model::polygon<bg::model::d2::point_xy<double> > poly3;
+    bg::read_wkt("POLYGON((1 1,0 -4,-4 -4,-4 0,1 1))", poly3);
+    check_touches = bg::touches(poly1, poly3);
+    if (check_touches) {
+         std::cout << "Touches: Yes" << std::endl;
+    } else {
+        std::cout << "Touches: No" << std::endl;
+    }
+
+    return 0;
+}
+
+//]
+
+
+//[touches_output
+/*`
+Output:
+[pre
+Touches: Yes
+Touches: No
+]
+*/
+//]