Appending to the output file rather than resetting the whole file.

[jalotra]

If a user runs the same passgen.py with different tags and names, I want new tag -a to be made that appends new passwords to the output.txt instead of clearing and then rewriting the whole file.

How to reproduce: python passgen.py roger -n -f -o Roger_all_combinations.txt wc -w roger_all_combinations.txt // Will give 38 python passgen.py roger -n -f -o roger_all_combinations.txt wc -w roger_all_combinations.txt // Will give 192