added operateOn to sugar.nim to give Nim the chaining mechanism it de… (#13092)

* implemented the with stdlib module as specified in https://github.com/nim-lang/RFCs/issues/193
* change sugar.outplace to sugar.dup according to https://github.com/nim-lang/RFCs/issues/193
* changelog update

lib/std/private/underscored_calls.nim

@@ -0,0 +1,38 @@
+
+#
+#
+#            Nim's Runtime Library
+#        (c) Copyright 2020 Andreas Rumpf
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## This is an internal helper module. Do not use.
+
+import macros
+
+proc underscoredCall*(n, arg0: NimNode): NimNode =
+  proc underscorePos(n: NimNode): int =
+    for i in 1 ..< n.len:
+      if n[i].eqIdent("_"): return i
+    return -1
+
+  if n.kind in nnkCallKinds:
+    result = copyNimNode(n)
+    result.add n[0]
+
+    let u = underscorePos(n)
+    if u < 0:
+      result.add arg0
+      for i in 1..n.len-1: result.add n[i]
+    else:
+      for i in 1..u-1: result.add n[i]
+      result.add arg0
+      for i in u+1..n.len-1: result.add n[i]
+  else:
+    # handle e.g. 'x.dup(sort)'
+    result = newNimNode(nnkCall, n)
+    result.add n
+    result.add arg0
+