Add common known good pcre patterns

[travisbgreen]

style guide could use some common pcre patterns as a cheat sheet such as:

pcre:"/^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})/";