SDL2 examples port

[rodneyp290]

This pull request replaces HawkNL with SDL2. Addresses issue #3

Note:

• Had to use 224.0.0.1 (LAN) multicast address to get it to work, although I'm just using my home router with no special set up (I'm not that familiar with multicast)
• It is usual recommended to use the output of sdl2-config --cflags & sdl2-config --libs during compilation, however I was unsure if that would work in the premake5 build script, especially cross platform. This means the include statements are written as #include <SDL2/SDL_XXX.h rather than #include <SDL_XXX.h>, which is all that is required when using sdl2-config -cflags output that includes "-I/path/to/SDL2/" amendment

[leif81]

Thanks so much @rodneyp290! Taking a look.