Jekyllify the site

This PR converts the static content that @haileypate wireframed into a standard Jekyll site structure.

* Updates the Jekyll config to include only the settings we care about

* Adds site-wide metadata to Jekyll config for easy inclusion into other pages (site name, tagline, contact info, etc)

* Adds a blog page that displays excerpts and links to the last 5 posts based on the contents of `_posts`

* Adds a projects page that displays all of the projects defined in `_data/current_projects.yml` that I stubbed out

* Adds stubbed out Markdown versions of pages that contain pure content (About Us, etc)

* Adds stubbed out HTML versions of pages that will contains forms, 3rd party integration (Contact Us, Calendar, etc.)

* Moves JS, CSS, and fonts to `assets/` to keep things a bit more organized

* Adds `README.md` file with local development instructions

* Adds basic `CONTRIBUTING.md` file with guidelines for [contributing to the site](https://github.com/blog/1184-contributing-guidelines)