Modify <head>

Currently, there is no way to dynamically modify `<head>` elements of a page, such as a title, and resource links.

Here is a simple way that this could be done, similar to: https://svelte.technology/guide#svelte-head
```mint
  fun render : Html {
    <head>
      <link rel="dns-prefetch" href="https://cdn.varvy.com">
    <head>

    <div>
      <{ "Hello" }>
    </div>
  }
```
