Add unique disqus_identifier

Use an optional `uuid` YAML variable to uniquely identify a page for Disqus. This helps match comments with a post in the event of changing page URL, domain, etc. See http://help.disqus.com/customer/portal/articles/472098-javascript-configuration-variables#disqus_identifier
Generate uuid for posts

Generate UUID for unique identifier
Alphabetize tag listing. Fixes #10
Enable Pygments pre Jekyll 2.0
- GitHub Pages doesn't support highlighter: pygments, wait to switch
Override author details per post
- Fixes #70
Fix syntax highlighting in post
Display the default image in case the avatar not available

Note that whenever content is written by another author, the existence of an avatar for that author is questionable, so adding another if-else block ensures that instead of the alt, the default image is shown
Merge remote-tracking branch 'origin/patch-1' into uuid
Merge remote-tracking branch 'origin/patch-2' into uuid
Merge pull request #72 from icyflame/master

Display the default image in case the avatar not available
Don't load Disqus script on pages that don't require it
- Was loading Disqus in the script.html include even when a shortname wasn't specified
Combine if statements
Fix typo on theme setup page.
Merge pull request #76 from kevinwang/fix-theme-setup-typo

Fix typo on theme setup page.
Add Magnific Popup
- Image links now display in a lightbox
Add Jekyll and Proofer tests
Add Travis badge
Merge pull request #78 from penibelst/travis

Add build and links test
Escape page title
Fix broken links and add missing alt descriptions