Implement super script tags

For most people, when they are putting in the degree character (15 °C) They actually use a superscript `o` tag instead:

```
			<w:r>
				<w:rPr>
					<w:rFonts w:ascii="Arial" w:cs="Arial" w:hAnsi="Arial"/>
					<w:vertAlign w:val="superscript"/>
				</w:rPr>
				<w:t xml:space="preserve">o </w:t>
			</w:r>
```

Implement the `sup` tag in HTML to handle this.