Create -a option

Add a feature to enable managing multiple configs in `~/.earthquake/***/`.
You can achieve this by using absolute path like `earthquake ~/.earthquake/foo`, but I think it is inconvenient.
So I added `-a` option to ease managing multiple configs.

### Usage
```bash
$ earthquake -a foo
```
It will create `~/.earthquake/foo`, and you can reuse the config by the same command from any directory.