Specify the character encoding using meta charset

* Use the shorter `<meta charset="utf-8">` to specify
  the character encoding instead of the longer
  `<meta http-equiv="content-type" content="text/html; charset=utf-8"/>`.

  For more in-depth information about how the character
  encoding of HTML documents is determined, please see:
  http://blog.whatwg.org/the-road-to-html-5-character-encoding.

* Specify the `<meta>` tag as early as possbile.

  For more information on why this is important see:
  https://github.com/h5bp/html5-boilerplate/blob/973b8453ded68af1d9c833d4ad4312e6c63ccbeb/doc/html.md#the-order-of-the-title-and-meta-tags
Place <meta http-equiv> tag in the right place

The meta tag for compatibility mode
(<meta http-equiv="X-UA-Compatible" content="IE=edge">) needs to be
included before all other tags except for the `<title>` and the other
`<meta>` tags.

Ref: http://msdn.microsoft.com/en-us/library/cc288325.aspx
Remove unneeded `type="text/css"` and `/`

* Remove `type="text/css"` (this is the default value specified by
  HTML5 so, unless you need a different value than the default,
  you can simply omit the type attribute).

* Remove solidus (in HTML, using the solidus isn’t required:
  http://dev.w3.org/html5/spec-author-view/syntax.html#syntax-start-tag)
Rename `emoji.gif` → `emoji.png`

`emojis.gif` is actually a PNG image:

   $ file emojis/emoji.gif
   emojis/emoji.gif: PNG image data, 22074 x 24, 8-bit/color RGBA
Losslessly optimize images

 original size:     3.3 MB (3478391 B)
 gzipped size:      2.1 MB (2150527 B)
 ─────────────────────────────────────
 reduction:         1.3 MB (1327864 B) [38.17%]

 * size = the combined size of all PNG images
Specify the base language of the document
Never empty
use the glyph instead of images
:fire: the emoji image files
Merge branch 'alrra-minor-improvements' into gh-pages