Merge pull request #25 from marcusva/master

New  SDL_filesystem wrappers and automated tests for go test
- Add some handy build commands from go-gogadget for GNU and BSD make as well
  as Win32 platforms:

  - `make packages` builds all packages
  - `make test` executes all Go tests for all packages
  - `make coverage` creates the code coverage for the Go tests
  - `make bench` executes any test benchmarks (TBD) for the packages
  - `make clean` removes temp files and core dumps
  - `make` executes `make clean` and `make packages`