Add possibility to read from STDIN too

[seventyeight]

Really like this project. But i miss the way to handle things via STDIN. For instance now you can do this: curl -s https://i.redd.it/06ozylnfmm521.jpg | ./target/release/viu -w 70
It is the first time coding some Rust. Any review is welcome.

[atanunq]

Wow, this is amazing! Thank you so much for taking the time. I am definitely adding your idea to the project. However, I am afraid this will take some time. I am close to releasing a major update that deals with animated GIFs and I have already changed every possible line of code there is. After that is done I will test out and include your changes.
Thanks again for contributing!

[atanunq]

Hey, @seventyeight! Your code is now live. I did alter a part of it to work around the changes needed for gif support, but the core stdin-reading logic is there. A thing I noticed is that you did not match some vital .unwrap() calls which is pretty important when app failure must be avoided. Overall great job and I look forward to hearing your ideas again!

[seventyeight]

Awesome! Thanks for the feedback. Appreciate it.