Accept HTML entities when parsing XML

Every once in a while, one of my feeds would throw an XML parse error
because it used ` ` or some other HTML entity. I feel Miniflux
should be lenient here, and Go already has a handy hook to make this
work.

reader/parser/format.go

@@ -27,6 +27,7 @@ func DetectFeedFormat(data string) string {
 	}
 
 	decoder := xml.NewDecoder(strings.NewReader(data))
+	decoder.Entity = xml.HTMLEntity
 	decoder.CharsetReader = encoding.CharsetReader
 
 	for {