func Example() {
	var fs http.FileSystem = http.Dir("assets")
	err := vfsgen.Generate(fs, vfsgen.Options{})
	if err != nil {
		log.Fatalln(err)
	}
}
This code will generate an assets_vfsdata.go file with
`var assets http.FileSystem = ...`
that statically implements the contents of "assets" directory.

vfsgen is great to use with go generate directives. This code can go in an assets_gen.go file, which can
then be invoked via "//go:generate go run assets_gen.go". The input virtual filesystem can read directly
from disk, or it can be more involved.
package vfsgen_test
import (
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"testing"
	"github.com/shurcooL/httpfs/union"
	"github.com/shurcooL/vfsgen"
	"golang.org/x/tools/godoc/vfs/httpfs"
	"golang.org/x/tools/godoc/vfs/mapfs"
)