add more test cases to sanitize-html.test.js

[ragnarokatz]

This issue was created as a result of fixing #458

Add more unit test cases to sanitize-html.test.js. This will serve as documentation as to how sanitize-html behaves according to different content passed in.

[KarlaChen]

@ragnarokatz Tony and I are going to add more test for it.

[humphd]

It would be helpful to take a look at the actual HTML being sent to our server now, and write some cases for things people actually do in their posts.