There were a lot of elements previously, like `Em`, `H1`, and a lot more, that took a string as the first argument previously. This was weird when you wanted to mix elements to output html like `<strong><em>…</em></strong>` or `<h1>Something <em>something</em> something</h1>`. gomponents is not an HTML validator, so I want people to be able to use elements however they please, also without text content.
This also means that all elements now have the same API.
This makes it clearer that the helpers return a `Node` of any kind, and that the type is not important.
This also streamlines the API, as attribute helpers already return just `Node`.
`a`, `form`, `img`, `input`, `label`, `option`, `progress`, `select`, and `textarea` are now just regular elements (without helper parameters), because:
- Sometimes the use case doesn't fit (`a` as anchor without href, for example)
- There's no reason these are special among the others, so streamlining them makes sense
Also added new attributes `action`, `alt`, `for`, `method` that I had somehow missed.
This makes it easier to use dot-imports.
Also updated the readme and examples with new usage, and move the `Classes` helper into the `components` package.
