This PR fixes #686 by adding the ability to compare media-types and report response-media-type-changed when the new media type is contained in the original one.

For example:

• application/atom+xml is contained in application/xml
• application/problem+json is contained in application/json
• image/svg+xml is contained in image/xml

Note:

• The part after the + is called a suffix as explained here: https://en.wikipedia.org/wiki/Media_type#Suffix
• This PR won't support multiple suffixes: https://www.ietf.org/archive/id/draft-ietf-mediaman-suffixes-01.html