Create data_path if it doesn't exist

When `mysteryshack` is started, but the directory stated by `data_path`, doesn't exist, it fails with the error:
> Failed to parse config: No such file or directory (os error 2)

`mysteryshack` should create the directory if it doesn't exist.

__To reproduce__
1. Edit `config` and set "data_path = hello"
2. Run `./mysteryshack serve`