add insert benchmark comparing StringSet to BroTree (StringSet is just a few ms faster for this)

bench/conv-words.sml

@@ -0,0 +1,33 @@
+val inIo = TextIO.openIn "words.txt"
+val outIO = TextIO.openOut "words.sml"
+
+fun readLines (inIo, acc) =
+  case TextIO.inputLine inIo of
+    SOME word => readLines (inIo, word :: acc)
+  | NONE => List.rev acc
+
+fun writeLines (outIO, lst) =
+  case lst of
+    [] => ()
+  | word :: tl =>
+      let
+        val word = String.substring (word, 0, String.size word - 2)
+        val isLast = tl = []
+        val word =
+          if isLast then "\"" ^ word ^ "\""
+          else "\"" ^ word ^ "\",\n"
+        val _ = TextIO.output (outIO, word)
+      in
+        writeLines (outIO, tl)
+      end
+
+fun main () =
+  let
+    val lst = readLines (inIo, [])
+    val _ = TextIO.output
+      (outIO, "structure WordsList = \nstruct \n val words = #[\n")
+    val _ = writeLines (outIO, lst)
+    val _ = TextIO.output (outIO, "]\n end")
+  in
+    ()
+  end