Update .gitignore
Nothing but sub main
Simple makefile

Commands:
'make dirs' - Creates required dirs
'make' - Compiles /src/*.cpp to /obj/*.o then compiles /obj/*.o to
/ballin.out
'make clean' - /obj/*.o and /ballin.out

Note:
- CFLAGS specifying c++11 standard
- Use of pkg-config for freetype2, libpng, and libglfw