Adding xmlns:content namespace to RSS feed and only write content:enc…

…oded if something on .Content (adityatelange#1411)

* Added xmlns:content namespace for valid RSS feeds with content:encoded

* Only write <content:encoded> in RSS if ShotFullTextinRSS and .Content has something

fixes: adityatelange#1385

layouts/_default/rss.xml

@@ -43,7 +43,7 @@
 {{- $pages = $pages | first $limit }}
 {{- end }}
 {{- printf "<?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"yes\"?>" | safeHTML }}
-<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
+<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:content="http://purl.org/rss/1.0/modules/content/">
   <channel>
     <title>{{ if eq .Title site.Title }}{{ site.Title }}{{ else }}{{ with .Title }}{{ . }} on {{ end }}{{ site.Title }}{{ end }}</title>
     <link>{{ .Permalink }}</link>
@@ -73,7 +73,7 @@
       {{- with $authorEmail }}<author>{{ . }}{{ with $authorName }} ({{ . }}){{ end }}</author>{{ end }}
       <guid>{{ .Permalink }}</guid>
       <description>{{ with .Description | html }}{{ . }}{{ else }}{{ .Summary | html }}{{ end -}}</description>
-      {{- if site.Params.ShowFullTextinRSS }}
+      {{- if and site.Params.ShowFullTextinRSS .Content }}
       <content:encoded>{{ (printf "<![CDATA[%s]]>" .Content) | safeHTML }}</content:encoded>
       {{- end }}
     </item>