Auto-create directory, globbing

[RRMueller]

This is an awesome little tool, thanks for creating it - it works great!

I just added a couple things that you can review that I found useful for myself:

1. I added the ability to have the program create the output directory automatically instead of the user being required to create it before running the program.
2. I could not figure out how to get globbing to work, so I added that functionality in when one of the args.files is "*.dm"
3. I have it checking if the file extension is ".dm" before attempting to decrypt it to lessen errors.

I'm a c/c++ programmer by day, so my apologies if the python is rough. Feel free to improve, adapt, or ignore this PR completely.

~Ryan