Update to github.com/go-gl/glow/gl/2.1/gl package.

Remove gist5286084 dot import.
gofmt -w -r 'gl.Int -> int32' ./
gofmt -w -r 'gl.Sizei -> int32' ./
gofmt -w -r 'gl.Uint -> uint32' ./
gofmt -w -r 'gl.Ubyte -> byte' ./
gofmt -w -r 'gl.Float -> float32' ./
gofmt -w -r 'gl.Double -> float64' ./
gofmt -w -r 'gl.GoStringUb -> gl.GoStr' ./
gofmt -w -r 'gl.Pointer -> gl.Ptr' ./
gofmt -w -r 'gl.Ptr(&x[0]) -> gl.Ptr(x)' ./
gofmt -w -r 'gl.Sizeiptr(x) -> x' ./
goimports -w ./