Added scaffolding

This is from https://github.com/TheLartians/ModernCppStarter/

all/CMakeLists.txt

@@ -0,0 +1,19 @@
+# SPDX-FileCopyrightText: 2023 github.com/TheLartians
+#
+# SPDX-License-Identifier: CC0-1.0
+
+# this script adds all subprojects to a single build to allow IDEs understand the full project
+# structure.
+
+cmake_minimum_required(VERSION 3.14...3.22)
+
+project(BuildAll LANGUAGES CXX)
+
+include(../cmake/tools.cmake)
+
+# needed to generate test target
+enable_testing()
+
+add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/../standalone ${CMAKE_BINARY_DIR}/standalone)
+add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/../test ${CMAKE_BINARY_DIR}/test)
+add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/../documentation ${CMAKE_BINARY_DIR}/documentation)