new formula: onetime

New formula: onetime. Assists users in creating one-time pads. Still actively supported upstream, and has gathered a lot of renewed interest thanks to Hak5 covering the tool recently.

(*This is my first formula created entirely from scratch, and I'm pretty thrilled to have actually managed to make it work around Homebrew's syntax & formula requirements. Extremely thoroughly tested, so hopefully will pass the build bot first time*).
Oh, yeah, I knew that. Why didn't I realise that. Ugh. Technology finds new ways to make my knowledge of it feel like I'm barely touching the surface every day heh.

So should 

```
system("#{bin}/onetime") && ("--version")
```

be working?