Allow selecting image type via Regexp

For example, SVG images might be of type "image/svg" or "image/svg+xml"

lib/manifique/metadata.rb

@@ -43,7 +43,13 @@ module Manifique
       end
 
       if options[:type]
-        results.reject! { |r| r["type"] != options[:type] }
+        if options[:type].is_a?(String)
+          results.reject! { |r| r["type"] != options[:type] }
+        elsif options[:type].is_a?(Regexp)
+          results.reject! { |r| r["type"].match(options[:type]).nil? }
+        else
+          raise ArgumentError, "Type must be a string or a regular expression"
+        end
       end
 
       if options[:sizes]