add the --verify option

This is attempt to fix #535. Since I'm new to the project, its structure and coding guidelines I'm sure that there are plenty of missing / incorrect things. Will be happy to amend those based on the code review. More specifically:
* I'm not sure what is a policy when it comes to testing CLI code as I couldn't find many tests for this test;
* it seems to me like the lib/blackList.js file could be a npm module on its own but would like to have your feedback here.