First Rust release

I rewrote the original Python script using Rust (but you can still find it here https://github.com/Pitasi/dyn-wallpaper/tree/old-python).
I've done this because of two main reasons:

• I wanted to try Rust (it's so cool!)
• A single binary it's so easier for people to use

But there are other benefits: on my laptop the "blending process" of merging two images now takes 10 times less time.

Warning: the Mac OS version has not been tested.

Download the binary for your platform, execute it from a terminal, and that's it. Check the README for downloading a set of wallpapers and start using it.