Allow `features` to take a list of dictionaries

For certain purposes (e.g., when writing a book), it's much easier to show a single file (the config file) rather than both the config file and the features CSV file if you want to talk about signs and transforms. It'd be really nice if `features` accepted a list of dictionaries like so:

```json
...
"features": [{"feature": "LOGWORDS", "sign": 1, "transform": "raw"},
{"feature": "LOGTYPES", "sign": 1, "transform": "raw"}]
...
```