Add heroku-remotes executable

I create staging and production remotes over, and over again. This
executable wraps my convention for naming Heroku apps.

Example:

When working on a GitHub-hosted repo at
`git@github.com:jcf/jcf-web.git`, the following Heroku apps would exist:

```
production git@heroku.logi.cl:jcf-web-production.git
staging    git@heroku.logi.cl:jcf-web-staging.git
```

I use `heroku.logi.cl` because I'm still using the Heroku accounts
plugin.