add examples

doc/snippets/Map_general_stride.cpp

@@ -0,0 +1,5 @@
+int array[24];
+for(int i = 0; i < 24; ++i) array[i] = i;
+cout << Map<MatrixXi, 0, Stride<Dynamic,2> >
+         (array, 3, 3, Stride<Dynamic,2>(8, 2))
+     << endl;

doc/snippets/Map_inner_stride.cpp

@@ -0,0 +1,5 @@
+int array[12];
+for(int i = 0; i < 12; ++i) array[i] = i;
+cout << Map<VectorXi, 0, InnerStride<2> >
+         (array, 6) // the inner stride has already been passed as template parameter
+     << endl;

doc/snippets/Map_outer_stride.cpp

@@ -0,0 +1,5 @@
+int array[12];
+for(int i = 0; i < 12; ++i) array[i] = i;
+cout << Map<MatrixXi, 0, OuterStride<Dynamic> >
+         (array, 3, 3, OuterStride<Dynamic>(4))
+     << endl;

doc/snippets/Map_simple.cpp

@@ -0,0 +1,3 @@
+int array[9];
+for(int i = 0; i < 9; ++i) array[i] = i;
+cout << Map<Matrix3i>(array) << endl;