cli does not provide informative message if invalid parameter supplied

[jo-tham]

it would be ideal if the cli identifies the invalid parameter, ouput instead of giving the full help menu

root@2996228a1857:/opt/learn# learn varsel --xy-data tests/integration/input/data_xy.csv --config tests/integration/input/vsel_xy_config.csv  --ouput output

Usage:
    learn describe (--xy-data <file>) [--quantile-type <string> --format <string> --output <dir>]
    learn varsel (--xy-data <file> --config <file>) [--yvar <string> --iteration <solutions:x-min:x-max> --criteria <string> --output <dir>]
    learn lda (--xy-data <file> --config <file>) [--yvar <string> --output <dir>]
    learn discrat (--xy-data <file> --x-data <file> --dfunct <file> --idf <file> --varset <int>) [--yvar <string> --output <dir>]

root@2996228a1857:/opt/learn# ls
bin		       codeship-steps.yml  Dockerfile  learn		   pylearn.log	README.md   rlibs     tests
codeship-services.yml  docker-compose.yml  env	       learn_cli.egg-info  pysite	rlearn.log  setup.py