Support embedding video using `<video>`

This also prepares us for different providers, e.g. vimeo.

go/blog/blog.go

			if err != nil {
				exit(fmt.Errorf("invalid video url '%s'", post.URL))
			}
			id := u.Query().Get("v")
			if (u.Host != "youtube.com" && u.Host != "www.youtube.com") || id == "" {
			var provider string
			switch {
			case strings.HasSuffix(u.Path, ".mp4") || strings.HasSuffix(u.Path, ".ogv"):
				provider = "native"
			case (u.Host == "youtube.com" || u.Host == "www.youtube.com") && u.Query().Get("v") != "":
				provider = "youtube"
				post.URL = fmt.Sprintf("https://www.youtube.com/embed/%s", u.Query().Get("v"))
			default:
				exit(fmt.Errorf("unsupported video url '%s'", post.URL))
			}
			post.URL = id
			err = videoTmpl.Execute(out, post)
			p := struct {
				Post
				Provider string
			}{post, provider}
			err = videoTmpl.Execute(out, p)
		default:
			fmt.Fprintf(os.Stderr, "Error: no output for type '%s'\n", post.Type)
			os.Exit(1)
var videoTmpl = template.Must(baseTmpl.New("video").Parse(`
<article id="{{ .Id }}" class="{{ .Type }}" {{- if .Tags }} data-tags="{{ json .Tags }}"{{ end }}>
	{{- template "title" . }}
	<iframe width="560" height="315" src="https://www.youtube.com/embed/{{ .URL }}" frameborder="0" allowfullscreen></iframe>
	{{ if (eq .Provider "youtube") -}}
	<iframe width="560" height="315" src="{{ safe_url .URL }}" frameborder="0" allowfullscreen></iframe>
	{{- else -}}
	<video src="{{ safe_url .URL }}" controls></video>
	{{- end }}
	{{- if .Content }}
	{{ markdown .Content }}

go/blog/blog.yaml

  date: 2016-09-26
  tags: [ideas, feature, "author:lu"]
  type: text
- url: file:///home/lu/m/video/films/Over The Garden Wall/OtGW-S01E01.mp4
  type: video