Write a program calendar that outputs a monthly calendar for a given month and year into a file.
Calendar by F. Last
Enter month year? 10 2019
10-2019.txt generated.
Output file: 10-2019.txt
October 2019
Sun Mon Tue Wed Thu Fri Sat
---------------------------------
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31