Use standard XML escaping

lib/pure/xmltree.nim

@@ -492,8 +492,7 @@ proc addEscaped*(result: var string, s: string) =
     of '>': result.add(">")
     of '&': result.add("&")
     of '"': result.add(""")
-    of '\'': result.add("'")
-    of '/': result.add("/")
+    of '\'': result.add("'")
     else: result.add(c)
 
 proc escape*(s: string): string =
@@ -508,8 +507,7 @@ proc escape*(s: string): string =
   ##  ``>``          ``>``
   ##  ``&``          ``&``
   ##  ``"``          ``"``
-  ##  ``'``          ``'``
-  ##  ``/``          ``/``
+  ##  ``'``          ``'``
   ## ------------    -------------------
   ##
   ## You can also use `addEscaped proc <#addEscaped,string,string>`_.