Update Button.swift

[bgisme]

When using libraries like Bootstrap, I often need to put child elements inside buttons. But the init() only takes contents.

Not sure if it was intentional. To only allow users to create Buttons with String contents. But I would think all Tags should have a designated init() that allows for children with a builder parameter, whether or not it produces well written HTML. And then the convenience inits would implement preferred or common usage. Like in A.swift where the convenience init() just takes contents.

[tib]

I agree, we should extend the Tag class and allow to create children by default for every single tag.

We can mark the init of those elements that can't have child elements with the @available(*, unavailable) attribute.

Give me some time, I'll experiment with this later on today won't merge this until that, since maybe we can have a better solution.

[tib]

I checked the Tag class for a generic init solution, but since it'd require the node it's quite hard to come up with something that would be useful for other subclasses. If we need we can extend other tags as well to support the builder param for now I'm going to merge this PR as it is.