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/rss/parser.go

@@ -17,6 +17,7 @@ import (
 func Parse(data io.Reader) (*model.Feed, *errors.LocalizedError) {
 	feed := new(rssFeed)
 	decoder := xml.NewDecoder(data)
+	decoder.Entity = xml.HTMLEntity
 	decoder.CharsetReader = encoding.CharsetReader
 
 	err := decoder.Decode(feed)