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*).
```
 inreplace "Makefile", '$(DESTDIR)/usr/bin/', '$(DESTDIR)/#{bin}' 
```
gets me

```
==> make install
install: /#{bin}: Permission denied
make: *** [install] Error 71
```

every time.