Added list tags command.

private/ptkutil.nim

@@ -0,0 +1,8 @@
+template first*(a: openarray): auto = a[0]
+
+template last*(a: openarray): auto = a[len(a)-1]
+
+proc flatten*[T](a: seq[seq[T]]): seq[T] =
+  result = @[]
+  for subseq in a:
+    result.add(subseq)