raise an explanatory error when the config is bad
raise an explanatory error when the config is bad

fixes #30
telmofcosta/analytical,jkrall/analytical,pedrocarrico/analytical,backupify/analytical,Seedrs/analytical,Bargains4Business/analytical,Bargains4Business/analytical,backupify/analytical,Bargains4Business/analytical,telmofcosta/analytical,Seedrs/analytical,Bargains4Business/analytical,jkrall/analytical