Link to Google Group rather than email

Link to the mailing list's Google Group so that people can easily peruse
historic messages, rather than providing the email address directly.
Add newline to end of main.css
Add spacing to pre and li elements

Add top and bottom margins to `li` and `pre` elements in posts.

Makes the layout much less cramped.
Prevent inline code blocks from wrapping

Prevent inline `code` elements from line-wrapping, which was ugly.