Render inline code snippets for notes

To make it nicer to read notes that contain backticks (that denote inline code snippets) we should actually wrap them in a <code> block.

This is a little nicer if we use an intermediary variable and output it finally, sanitised by safeHTML, rather than doing it at each point.

If a link appears in this <code>, it should be ignored by HTML-Proofer as <code>s are not checked.

Plus, make links that are embedded in inline code snippets (i.e. as part of notes that have URLs autolinked) more readable, we need to make the contrast better by introducing a lighter colour for the <a>s.