Styles for code, pre and kbd elements

[Edvins Antonovs]

Noticed several things, I might be worth to improve.

• Change pre background colour to #ebebeb because on some of the monitors you will hardly notice any difference between the #fff background and #f7f7f7.
• Add styling for <kbd> HTML element.
• Add more examples to http://potatocss.com/ docs
  • Inline-code
  • Block-code (already have the case for it)
  • Example with kbd

[Edvins Antonovs]

Possible solution: https://jsfiddle.net/0uL70p8f/2/