The 'Feature Profiles' section of the 'Client-Server API' specification
contains a table, showing whether a module is required or optional for
every profile. Previously the table was hard to read since "Required"
looks visually very similar to "Optional".
This commit improves the readability of the table by automatically
applying a darker background color to table cells containing "Required"
via a new Hugo shortcode.
Signed-off-by: Martin Fischer <martin@push-f.com>
