addQuitProc now works with closures, and c, js(node/browser) backend; fix some bugs in testament (#14342)

* make addQuitProc great again

* fix bugs in testament

* fix test

* change 2016 => 2020

* addQuitProc => addExitProc + locks

* move to std/exitprocs

lib/pure/quitprocs.nim

@@ -1,28 +0,0 @@
-#
-#
-#            Nim's Runtime Library
-#        (c) Copyright 2016 Andreas Rumpf
-#
-#    See the file "copying.txt", included in this
-#    distribution, for details about the copyright.
-#
-
-## ``system.addQuitProc`` is nice and very useful but due to its C-based
-## implementation it doesn't support closures which limits its usefulness.
-## This module fixes this. Later versions of this module will also
-## support the JavaScript backend.
-
-var
-  gClosures: seq[proc () {.closure.}]
-
-proc callClosures() {.noconv.} =
-  for i in countdown(gClosures.len-1, 0):
-    gClosures[i]()
-
-proc addQuitClosure*(cl: proc () {.closure.}) =
-  ## Like ``system.addQuitProc`` but it supports closures.
-  if gClosures.len == 0:
-    addQuitProc(callClosures)
-    gClosures = @[cl]
-  else:
-    gClosures.add(cl)