Use htmlparser2 instead of htmlparser.
html5 parser is not a real dev dependency.

This was added so that people could run tests against it, but really, if you want to run tests against alternate HTML parsers, you should install them yourself.
Simplify default-parser–finding logic.

This was needlessly complicated.
Remove test that shouldn't exist.

This markup is not invalid; browsers, and now htmlparser2, can deal fine.
Fix broken test.

A missing closing quote was making the `<script>` tag not get parsed. Bad news.
Add test for unclosed <td>s. Fixes #605.
Add test for innerHTML of <script> tags. Fixes #575.
Add test for attributes containing < and >. Fixes #494.
Add test for multiline attributes. Fixes #585.
Add test for empty attributes. Fixes #488.
Add tests for omitting optional closing tags. Fixes #482.
Allow more attribute names. Fixes #368, fixes #5.