Suggestion: bake resource path into executables

Upon first usage, it is not clear that the CWD has to be the project root -- running speedtest & co. from the build directory just causes them to crash, and one has to debug to find out why.

Since they are not shipped, CMake's `CMAKE_CURRENT_SOURCE_DIR` could be set as a define so that the path to `cryteksponza.bin` is not relative, but absolute.

