Rewrite xmltools.innerText

Make it recursive, define for node types other than xnElement

tests/stdlib/txmltree.nim

@@ -1,6 +1,11 @@
 discard """
   file: "txmltree.nim"
-  output: "true"
+  output: '''true
+true
+true
+true
+true
+'''
 """
 
 import xmltree, strtabs
@@ -9,5 +14,14 @@ var x = <>a(href="nim.de", newText("www.nim-test.de"))
 
 echo($x == "<a href=\"nim.de\">www.nim-test.de</a>")
 
+echo(newText("foo").innerText == "foo")
+echo(newEntity("bar").innerText == "bar")
+echo(newComment("baz").innerText == "")
 
-
+let y = newXmlTree("x", [
+  newText("foo"),
+  newXmlTree("y", [
+    newText("bar")
+  ])
+])
+echo(y.innerText == "foobar")