use toml instead of ini format for parameters

[kireet]

right now the code uses configparser/ini format for parameters. toml could be a better fit as it's still quite readable and allows for some structure. one use case i had recently was enabling/disabling featurizers. with the ini format, i had to create a dumb enabled flag in the featurizer and then set all the featurizer enabled flags for every experiment. it worked but was a hassle.

with toml, we could just have

featurizers=["$f1", "$f2"] 

as config. we'll need to provide some clear documentation though, as in this case the json experiment file will refer to the $featurizers parameter in the config file while the config file will refer to $f1 in the experiment file...