Feature/strict mode

This is a duplicate of [lchenays add strict mode pull request](https://github.com/cucumber/cucumber-js/pull/204), but with fixed/added tests for the new strict flag.
I also modified the --help message for the new flag to be inline with Ruby cucumber.
@aslakhellesoy Sorry I don't see it?
Looks like I/my editor dropped the `");` down to a newline, was that it? Happy to move it back.