feat(enforce): ensure commit convention, by using a commit hook

this feature creates, if it doesn't exist, a pre-commit-hook to ensure that the user is using the convention. the validator/commit-hook is taken from [here](https://github.com/angular/angular.js/blob/master/validate-commit-msg.js). 

Could somebody check that on Windows? I am not sure `fs.chmod(.., '0755')` really works on that OS. Thanks!