HTML Proofer: Ignore missing alt tags

 - The OGPL logo is tagged with a following span
 - Silencing the img/feature content till they can be looked at in gh-99
Merge pull request #100 from nschonni/alt-tag-fixes

HTML Proofer: Ignore missing alt tags
Fix: Blog link references

The posts had different dates, but all the URLs were pointing to
2013-06-11
Merge pull request #101 from nschonni/permalink-fixes

Fix: Blog link references