Fix a number of empty links

[pepelsbey]

Search for <a href="" in *.md

• [ ] blog/_posts/2010-01-27-nalakuvara-a-user-customized-opera-desktop-package.md
• [ ] blog/_posts/2010-04-13-making-your-site-mobile-friendly-rit-2010-moscow.md
• [ ] blog/_posts/2010-04-23-opera-10-52-final-for-mac-is-out.md
• [ ] blog/_posts/2010-11-15-how-to-get-started-contributing-to-opera-dragonfly-development.md
• [ ] blog/_posts/2011-10-06-bruces-fronteers-presentation-html5-semantics.md