Add support for video (youtube) posts

go/blog/blog.go

	"html/template"
	"io"
	"io/ioutil"
	"net/url"
	"os"
	"strings"
	"github.com/russross/blackfriday"
	"gopkg.in/yaml.v2"
			err = songTmpl.Execute(os.Stdout, post)
		case "text":
			err = textTmpl.Execute(os.Stdout, post)
		case "video":
			if !strings.HasPrefix(post.URL, "https://www.youtube.com/watch") {
				exit(fmt.Errorf("can't handle video '%s'", post.URL))
			}
			u, err := url.Parse(post.URL)
			if err != nil {
				exit(fmt.Errorf("invalid video url '%s'", post.URL))
			}
			id := u.Query().Get("v")
			if id == "" {
				exit(fmt.Errorf("invalid video url '%s'", post.URL))
			}
			post.URL = id
			err = videoTmpl.Execute(os.Stdout, post)
		default:
			fmt.Fprintf(os.Stderr, "Error: no output for type '%s'\n", post.Type)
			os.Exit(1)
</article>
`))
var videoTmpl = template.Must(template.New("video").
	Funcs(funcs).Parse(`
<article id="{{ .Id }}" class="video">
	{{- if .Title }}
	<header>
		<h1>{{ .Title }}</h1>
		{{- if .Date }}<time>{{ .Date }}</time>{{ end -}}
	</header>
	{{- end }}
	<iframe width="560" height="315" src="https://www.youtube.com/embed/{{ .URL }}" frameborder="0" allowfullscreen></iframe>
	{{- if .Content }}
	{{ markdown .Content }}
	{{- end -}}
</article>
`))
func exit(err error) {
	fmt.Fprintf(os.Stderr, "Error: %s\n", err)
	os.Exit(1)

go/blog/blog.yaml

    are optional.
  date: "2016-09-25"
  type: text
- url: https://www.youtube.com/watch?v=yLuOzNeHw5I
  content: Lights, by Archive.
  type: video