add answer tag

[alanarnholt]

I would be nice to have the answers to questions or exercises be easily distinguishable from the rest of the text. I would ask students to use the answer tag for all of their answers with a small explanation at the start of the lab about using a tag that might look something like:

`

Complete all Exercises. Surround your answers to all questions and exercises with an answer tag:

<div id="answer">
your answer here
</div>

`