Markup inside comments

There is a bug that is pretty disastrous if you have markup inside of html comments. The result will be that the opening comment '<!--' is not parsed, the markup inside is, and then the closing comment '-->' is replaced. The comment is left open and comments out the rest of the page.

Changes:
* Modify the regex to leave comments intact
* Switch to using `tap` for tests
* Update tests with example input

I can see cases where you would also want to strip out comments, and this regex would need to be modified to do that. The case I am using it for, the browser, it doesn't matter because the comments won't appear. 

The reason why I updated to use `tap` is that the dependency tree is much smaller and pure js. I don't want to impose on your project, but it didn't seem like there was a huge advantage to use `fox` over `tap`. If you want to run in the browser you can also have the same tests use `tape` and run them on [Testling](http://ci.testling.com/). I can help out with that if you like.