Escape ' and / when using escape in xmltree

lib/pure/xmltree.nim

@@ -151,6 +151,8 @@ proc addEscaped*(result: var string, s: string) =
     of '>': result.add(">")
     of '&': result.add("&")
     of '"': result.add(""")
+    of '\'': result.add("'")
+    of '/': result.add("/")
     else: result.add(c)
 
 proc escape*(s: string): string = 
@@ -164,6 +166,8 @@ proc escape*(s: string): string =
   ##  ``>``          ``>``
   ##  ``&``          ``&``
   ##  ``"``          ``"``
+  ##  ``'``          ``'``
+  ##  ``/``          ``/``
   ## ------------    -------------------
   result = newStringOfCap(s.len)
   addEscaped(result, s)