Option to remove row label emphasis in tables

[GarenSidonius]

See https://stackoverflow.com/questions/24090573/how-to-remove-the-emphasis-characters-on-row-names-when-using-pandoc-in-r

This option is important because professional tables typically do not have bolded or italicized row labels (e.g., see examples in Ch. 3 of Chicago Manual of Style). The response on StackOverflow suggests a workaround, but pander will be more useful if it can produce professional tables without a workaround.