Add raw_html parameter to Styler.format, enabling richer output

could be used to turn a column of values into a column of links to English Wikipedia articles, when exported with to_html.

To achieve this, we would need to always pass raw HTML to the jina templates, changing how formatting is currently done in Styler.to_html.

Formats performed with raw_html=True would have no effect on Styler.to_excel.