Adds a content-type header to response. See: wrap-content-type.

Middleware that adds a content-type header to the response if one is not
set by the handler. Uses the ring.util.mime-type/ext-mime-type function to
guess the content-type from the file extension in the URI. If no
content-type can be found, it defaults to 'application/octet-stream'.

Accepts the following options:

:mime-types - a map of filename extensions to mime-types that will be
              used in addition to the ones defined in
              ring.util.mime-type/default-mime-types