Improve font rendering in code examples
Improve font rendering in code examples

This changes the monospaced font-stack to use the system typeface in code examples, only prefering Menlo.
tleskin/guides,nicobot/guides,skaterdav85/guides,davidpett/guides,knownasilya/guides,skaterdav85/guides,knownasilya/guides,MarkMT/guides,tleskin/guides,HeroicEric/guides,skaterdav85/guides,jkarsrud/guides,MarkMT/guides,jkarsrud/guides,jkarsrud/guides,tleskin/guides,HeroicEric/guides,MarkMT/guides,davidpett/guides,knownasilya/guides,davidpett/guides,davidpett/guides,HeroicEric/guides,jkarsrud/guides,skaterdav85/guides,MarkMT/guides,knownasilya/guides,nicobot/guides,nicobot/guides