build(cmake): add the CMake package config and target files

Signed-off-by: k4yt3x <i@k4yt3x.com>

cmake/Video2XConfig.cmake.in

@@ -0,0 +1,2 @@
+@PACKAGE_INIT@
+include("${CMAKE_CURRENT_LIST_DIR}/Video2XTargets.cmake")

cmake/version.h.in

@@ -0,0 +1,7 @@
+#pragma once
+
+namespace video2x {
+
+#define LIBVIDEO2X_VERSION_STRING "@PROJECT_VERSION@"
+
+}  // namespace video2x