Allow `features` to take a list of dictionaries

[desilinguist]

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:

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