added playground project and made (again) the common.cmake behave when included multiple times
diff --git a/scripts/playground/CMakeLists.txt b/scripts/playground/CMakeLists.txt
new file mode 100644
index 0000000..c587a8e
--- /dev/null
+++ b/scripts/playground/CMakeLists.txt
@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.0)
+
+project(playground)
+
+include(../cmake/common.cmake)
+
+include_directories("../../doctest/")
+
+doctest_add_executable(${PROJECT_NAME} main.cpp test.cpp)
+
+doctest_add_test(NAME ${PROJECT_NAME} COMMAND $<TARGET_FILE:${PROJECT_NAME}>)