Add twittertimeline widget
add span class icon-label to twitter_timeline
Include instructions for twitter-timeline feature
Merge branch 'twitter-timeline' of https://github.com/chdoig/pelican-bootstrap3 into chdoig-twitter-timeline

* 'twitter-timeline' of https://github.com/chdoig/pelican-bootstrap3:
  Include instructions for twitter-timeline feature
  add span class icon-label to twitter_timeline
  Add twittertimeline widget