pg-info

Should be the first of many pg commands.

There's a basic heroku postgresql client in here, though I'd probably like to move it out to `heroku-go` as `heroku-go/postgresql` once it's a little more polished.

Before merging this, I'd like to make the `dbname` argument a little more flexible such that it can take only a color (without the `heroku-postgresql-` prefix) as so:

```bash
$ hk pg-info heroku-postgresql-crimson

$ hk pg-info crimson
```

I also need to update the styleguide.