Code cleanup and better project structure

[JMPerez]

I have made a several of changes

• Review code
  • Added missing ´var´
  • Use documentFragment to replace repeated DOM manipulation
  • Reduce dependency on jQuery
• Complete the Twitter example
• Added more examples in arguments section
• Implement listview sample
• Improve subscribe (adding unsubscribe)
• Improve navigation, so it always uses Spotify URIs and there is a link to go back
• Improve structure, so all sections are in their own page
• Improve maintainability. Now there is no need to have duplicated JS, CSS or HTML code in both encoded and unencoded flavours.
• Removed unused assets
• Optimized images
• Added app icon
• Added the possibility of select the source code to easy copy