util: backport scope_exit & co. from the Library Fundamentals TS v3

Implementation taken from scope-lite by Martin Moene,
commit 197cd4240069b2b8c393ad0d9eabdee601b606b4

Change-Id: I872b6821504b3270ebdc4c48b7255731fb2efc57
diff --git a/COPYING.md b/COPYING.md
index 7b140e4..b72dd74 100644
--- a/COPYING.md
+++ b/COPYING.md
@@ -12,6 +12,9 @@
 - optional-lite by Martin Moene is licensed under the
   [Boost Software License 1.0](https://github.com/martinmoene/optional-lite/blob/master/LICENSE.txt)
 
+- scope-lite by Martin Moene is licensed under the
+  [Boost Software License 1.0](https://github.com/martinmoene/scope-lite/blob/master/LICENSE.txt)
+
 - variant-lite by Martin Moene is licensed under the
   [Boost Software License 1.0](https://github.com/martinmoene/variant-lite/blob/master/LICENSE.txt)