Simplifications

This release has a lot of breaking changes, but it's worth it, I promise! We can now write HTML components in Go almost as if it's a DSL, but pure Go with all the benefits. 😎

⚠️ Breaking: All elements and attributes have been moved into a single package html. Because they're almost always used together, this makes perfect sense, and makes it easier to use dot imports. Unfortunately, because of name clashes, we now have FormEl/FormAttr, StyleEl/StyleAttr, and TitleEl/TitleAttr.
⚠️ Breaking: The Document element has been renamed Doctype.
⚠️ Breaking: a, form, img, input, label, option, progress, select, and textarea are now just regular elements (without helper parameters).