remove white text shadow around links and change aside to higher contrast gray

The link text was hard to read with the white text-shadow style on them, so I removed it to increase legibility. I also increased the contrast of the gray aside text from $gray-4 to $gray-2 to make it more readable as well. 

![PR reference screenshot](https://cloud.githubusercontent.com/assets/3051193/4999182/0a876cae-69ae-11e4-80c7-d537e575567d.png)