Reworked index.html

- Added `lang` attribute to `html` tag
- Replaced old charset meta tag with the new one
- Moved viewport meta tag further to the top to be recognized early
- Removed IE render engine meta tag (no longer needed)
- Commented out description meta tag while it's empty (TO DO!)
- Added HTML5 shiv to enable HTML5 support for <IE9
- Changed _browse happy_ notification to show on <IE9 instead of <IE8

__TO DO:__

- Add Google Analytics ID
- Add favicon.ico (or other shortcut icon file)
Reworked 404.html

- Removed most of the styles from the head-area
- Added a view lines to center the error message

The 404 page should be reworked with the other pages (TO DO!)
Added To do section to the README.md
Added shortcut icon link tag
Added shortcut icon link tag
Added to do entry: humans.txt
Added to do categories
Added to do entries
Merge pull request #1 from kleinfreund/master

Reworked html files / Added to do list to README.md