scripts for configuring env vars

Adds methods to manage the env between releases.

`bin/config set` to add individual settings, e.g.:
```bin/config set app prod FOO=bar BAZ=5```

`bin/config unset` to remove individual settings, e.g.:
```bin/config unset app prod FOO BAZ```

`bin/config put` to use a file as the environment, e.g.:
```bin/config put app prod ./.env```