added CMake support (#12)

This PR supplies some minimal CMake support, to make SDLpp available via CMake's FetchContent or CPM
Please supply a version (and maybe it is time to create a tag for the current version)

Cheers
Sebastian

Author: psyinf

CMakeLists.txt

@@ -0,0 +1,13 @@
+project(sdlpp VERSION 0.0 LANGUAGES CXX)
+
+
+
+add_library(${PROJECT_NAME} INTERFACE)
+add_library(${PROJECT_NAME}::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
+
+target_include_directories(
+  ${PROJECT_NAME}
+  INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
+            $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+)
+