Site author

Hey, so this pull request allows you to configure a default author for the site. You just add that person to `_config.yml`

```
author:
  name: Brian Wheeler
  link: brianw.io
  twitter: karrisaarinen
  gplus: 100687498195339762535
  bio: Co-founder, Design
  image: ks.png
```

I'm not sure if this fits into the direction you want this theme to go, but it was definitely a pain point for me as a developer, thought I'd make a pull request.