Twitter Cards support for this theme.

Reimplemented #102 mixing og and twitter tags.
Added Intellij files to gitignore
Merge branch 'twitter_cards' of https://github.com/torre76/pelican-bootstrap3 into torre76-twitter_cards

* 'twitter_cards' of https://github.com/torre76/pelican-bootstrap3:
  Twitter Cards support for this theme.
Some additional fixes
Fixed OG image
Removed all refs to deprecated static path and twitter and og images behave the same now
Separates index.html from a custom_article.html template.

This makes it simpler to change the index.html file in a derative of the template, overriding only the index page.
add spotify to non-square icon list
Merge pull request #115 from nevillelyh/master

add spotify to non-square icon list
Merge pull request #114 from unbrice/custom_index

Separates index.html from a custom_article.html template.
New examples encountered
Update EXAMPLES.md
Even more examples!

Google keeps on giving...
Add lang attribute to html tag, based on default lang and article/page lang
Refactoring of Open Graph metadata, and update of REAMDE
Add support for author, keywords and description meta tags
Improved Archives style
Add basic support for liquid tags plugin based IPython notebooks
Full IPython nb liquid tags support
Adds a link rel="canonical" to index, articles and pages.