LazSDL2Extensions package

SDL2Extended.lpk package is used to wrap SDL2 methods in easy to use objects.

For now I available objects:
* sdl.ext.stream.pas - wrapper around PSDL_RWops data structure to provide interface how SDL can read data from Lazarus TStream descendants
* sdl.extended.window.pas - wrapper around PSDL_Window structure. Provide many events to process many PSDL_Window operations
* sdl.extended.application.pas - wrapper around SDL_Event. Object calls SDL_PoolEvent to process all messages witch SDL2 could create.