V3 focus styles (accessibility) and fixes

Little fixes and:
- converted toggle menu link to button
- hover colors change mainly in menu and footer like codeigniter.com ones (better contrast and readability)
- css focus added (navigate using tab)
- a bit bigger logo (setup using height only, its adaptive, removed width attribute)
- quotes around font names
- lang attribute back

Author: Gianluigi Vizzielli