adding exercise 6.1
adding exercise 6.2
adding exercise 6.3
pattern matching used
added exercise 7.1
added exercise 7.2
added exercise 8.1
added a file from the exercise 7.2
added a file from the exercise 7.1
added exercise 8.2
added exercise 9.1
added exercise 9.1
added exercise 9.2
added exercise 9.3
added exercise 11.1
added exercise 10.1
added exercise 10.2
added exercise 10.3
added exercise 10.4
updating exercise 2.2