new rule: requireHyphenBeforeDescription

#50

This might need some more tests?

I'm assuming most people want the space so its like ` - description` not ` -description`

so it works like ` if (tag.description.substring(0, 2) !== '- ') {` 


Yeah the test cases in jscs itself probably aren't completely consistent but I see a lot of `should report on` and the describe usually the value of the option like `true`