execute and insert commands found in markdown inside ``` starting with #!

0.before.md

Hello world

#! ls -la

1.after.md

Hello world

#! ls -la
total 0
drwxr-xr-x   5 progrium  staff   170 Mar 23  2015 .
drwxr-xr-x  13 progrium  staff   442 Jun 14 14:31 ..
drwxr-xr-x  56 progrium  staff  1904 Aug 12 19:22 bin
drwxr-xr-x   3 progrium  staff   102 Mar 23  2015 pkg
drwxr-xr-x   9 progrium  staff   306 Jul 14 12:41 src

docshebang.go

package main

import (
	"fmt"
	"io/ioutil"
	"os"
	"strings"

	"github.com/lunixbochs/vtclean"
	"github.com/progrium/go-shell"
)

func main() {
	d, _ := ioutil.ReadAll(os.Stdin)
	doc := string(d)
	preparts := strings.SplitN(doc, "```\n#!", 2)
	postparts := strings.SplitN(preparts[1], "```", 2)
	cmdparts := strings.SplitN(postparts[0], "\n", 2)
	cmdline := strings.Trim(cmdparts[0], " ")
	output, _ := shell.Cmd(cmdline).OutputFn()()
	fmt.Println(
		strings.Join([]string{
			preparts[0],
			"```\n#! " + cmdline + "\n",
			vtclean.Clean(output, false),
			"\n```",
			postparts[1],
		}, ""))

}