Add jump bait to blog post excerpts

Using excerpts that are fully-formed sentences may confuse some potential readers. This would add an indicator link to each excerpt to view the full post. @sandersonet, thoughts?

![screenshot 2014-07-23 14 22 23](https://cloud.githubusercontent.com/assets/3422584/3680527/7b86326a-12af-11e4-8fda-ea59d94895b7.png)