Add gem for authors

* https://github.com/bellycard/middleman-blog-authors
* Add author.html.erb template
* Pull in author name on index page
* Add author section to footer
Move header styles into partial
Move footer and index styles to partial
Add layout for index page
Polish overall design and add About page

* Add accordian styles and markup on About page
* Adjust max-width in grid-settings
* Apply ul styles to Tags and Calendar pages
* Move _header to _navigation
* Style appearance of images in blog posts