Collect examples for chapters 7 and 8

chapter_03/examples/addables.cc

chapter_06/examples/ipsum.txt

chapter_06/examples/ranges0.cc

chapter_06/examples/strtrans.cc

chapter_07/PolyVal.cc

chapter_07/examples/polymorphic/1_virtual/CMakeLists.txt

chapter_07/examples/polymorphic/1_virtual/Circle.cc

chapter_07/examples/polymorphic/1_virtual/Circle.hh

chapter_07/examples/polymorphic/1_virtual/Point.cc

chapter_07/examples/polymorphic/1_virtual/Point.hh

chapter_07/examples/polymorphic/1_virtual/Polygon.hh

chapter_07/examples/polymorphic/1_virtual/Shape.hh

chapter_07/examples/polymorphic/1_virtual/Triangle.cc

chapter_07/examples/polymorphic/1_virtual/Triangle.hh

chapter_07/examples/polymorphic/1_virtual/main.cc

chapter_07/examples/polymorphic/2_any/CMakeLists.txt

chapter_07/examples/polymorphic/2_any/Circle.cc

chapter_07/examples/polymorphic/2_any/Circle.hh

chapter_07/examples/polymorphic/2_any/Point.cc

chapter_07/examples/polymorphic/2_any/Point.hh