Provide Godeps file for easy dependency installation

First: Thanks for this project, looks like a great addition to Sentinel! I got it up and running in a matter of seconds (well, after I figured out I need to `go get` this repo and then the dependencies).

You might want to consider managing your dependencies somehow.
[gpm](https://github.com/pote/gpm) is a nice little dependency manager for Go. It needs nothing more than the links in a `Godeps` file and a bash to execute in. The rest will be handled by gpm just fine.
The necessary Godeps file is bundled in this PR.

This simplifies the whole process of getting the project and running it to:

```
go get github.com/therealbill/redskull && cd $GOPATH/src/github.com/therealbill/redskull && gpm install && go build && ./redskull
```

(in case gpm is already installed)