Add example images for all filters and different sigma values

A2/images/astronaut/kirsch.jpeg

A2/images/astronaut/log_1.jpeg

A2/images/astronaut/log_1_5.jpeg

A2/images/astronaut/log_2.jpeg

A2/images/astronaut/log_3.jpeg

A2/images/astronaut/prewitt.jpeg

A2/images/astronaut/roberts.jpeg

A2/images/astronaut/sobel.jpeg

A2/images/chalsea/kirsch.jpeg

A2/images/chalsea/log_1.jpeg

A2/images/chalsea/log_1_5.jpeg

A2/images/chalsea/log_2.jpeg

A2/images/chalsea/log_3.jpeg

A2/images/chalsea/prewitt.jpeg

A2/images/chalsea/roberts.jpeg

A2/images/chalsea/sobel.jpeg

A2/images/coins/kirsch.jpeg

A2/images/coins/log_1.jpeg

A2/images/coins/log_1_5.jpeg

A2/images/coins/log_2.jpeg