Allow lst files to be written in json/yaml/toml/etc

[kadler]

Format would contain an array of dictionaries. This would allow us to drop the custom format and parsing code. AFAIK, the custom format was developed because it was easy to parse from a shell script, but if we're converting to Python (#70) it's easy to support various formats. Python has built-in support for INI and JSON, but YAML and TOML require external packages. IIRC, all these packages implement the pickle API so its all just load and dump to convert and just a matter of mapping the extension to the correct module (easy enough to do with a dictionary).

We should provide a utility which can convert the custom .lst to json/yaml/toml/etc.

I would recommend either YAML or TOML for the ones we ship.