Docs: update information about `print styles`

Fix: h5bp/html5-boilerplate#1386
Remove Google Frame message

As said at http://blog.chromium.org/2013/06/retiring-chrome-frame.html Google Frame was retired/obsolete.

Changed "chromeframe" class to "browsehappy"
Add vertical centering for audio-, canvas- and video-tags

Remove the gap between videos, audio and canvas and the bottom of
their containers by vertically centering the tags.

Closes #1326.
Remove Chrome Frame meta tag and HTTP header hints

See also `Retiring Chrome Frame - developer FAQ`:
https://developers.google.com/chrome/chrome-frame/

Close #1396.
Add `initial-scale=1` to meta viewport

iOS 6 fixes the infamous orientation change bug, so a better experience
is provided by reintroducing `initial-scale=1`.
Merge branch 'master' of https://github.com/h5bp/html5-boilerplate

# By Bommeli (1) and others
# Via Nicolas Gallagher
* 'master' of https://github.com/h5bp/html5-boilerplate:
  Add `initial-scale=1` to meta viewport
  Remove Chrome Frame meta tag and HTTP header hints
  Add vertical centering for audio-, canvas- and video-tags
  Remove Google Frame message
  Docs: update information about `print styles`