`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.
Previously, elements of kind void and empty elements generally would be rendered auto-closing (with a final `/` character in the start tag), which is allowed sometimes but arguably wrong. See https://dev.w3.org/html5/spec-LC/syntax.html#end-tags
This created problems with for example `textarea` and `script`, which cannot be auto-closing, or the browser renders it wrong.
Also clarified in the docs that this library outputs HTML5.
Fixes#42.
The Render function has been changed to take a `Writer` instead of returning a string. This makes it possible to generate documents without having the whole content in memory.
This also removes the `gomponents.Write` function, which is now redundant.
Furthermore, the `el.Document` function has been changed to only take one child, as multiple children never make sense for it. (It's not even a child, more a sibling.)
