Fix usage of <pre> in several places

[tripu]

• <pre> does not need <code>
• Extra spaces and carriage returns were messing with indentation and padding of <pre> blocks

[ashimura]

Regarding the proposed changes for 'w3c.json.html', I'm OK with all the following three points:

1. putting "{" right after "<pre>" and putting "}" right before "</pre>"
2. putting "<br/>" and another "<br/>" into two separate lines
3. removing "&nbsp;"s right before [[<pre>"group": [35422, 83907]</pre>]]

[tripu]

Assuming that's a 👍
🙂