Add test for entities within textarea
Make test pass

User input should never simply be unescaped. In this case, it could
enable XSS attacks if you put escaped tags into a textarea, because
upon minifying they would be unescaped.
Fix test name (since the underlying behavior changed)

The new behavior is correct according to HTML5 parsing and serialization
rules. A <textarea> can not contain other elements, if it does, that is
an error and the result should try to match the user’s intent. So, like
most browsers, HTML inside a <textarea> is properly escaped upon
parsing.
Merge pull request #65 from moeffju/feature/keep-entities-intact

Keep entities intact inside exempt tags