Add clearer documentation for valid keys to specify in parameter dictionaries passed to CFL

[iwahle]

The parameters that can be specified in the dictionaries passed through the block_params list are currently not well documented
in the API reference for CondDensityEstimators, CauseClusterers, or EffectClusterers. The expected keys can be found in the get_default_block_params method in Block class descendants, and in the get_default_model_params method of CDEModel and ClustererModel class descendants, but must be made much easier to access in the documentation.