podex: initial import

podex is a command line tool to bootstrap a kubernetes container manifests from docker image metadata.

Manifests can then be edited by a human to match deployment needs.

Example usage:
```
$ docker pull google/nodejs-hello
$ podex -yaml google/nodejs-hello > google/nodejs-hello/pod.yaml
$ podex -json google/nodejs-hello > google/nodejs-hello/pod.json
```

The `podex/manifests` subdirectory could also be used to host example pods for popular docker images.
I meant to do both, I'm OK to split the PR in 2.