- assigned _glfw-qualified private names to all static symbols to avoid naming conflicts when including glfw3impl.h
- added casts as needed to compile glfw3impl.h as C++
- replaced sprintf with snprintf to avoid warnings from clang -Wall, (except on win32, where this provokes an appveyor failure `'snprintf' undefined`)
- Added a brief remark on `glfw3impl.h` to the `Compiling GLFW` section in `README.md`
- Added `Garett Bass` to `CONTRIBUTORS.md`
