Cached GitHub data for the dashboard

As of the latest commit here the `projects.yml` file we already use for the dashboard is rewritten with GitHub data added as keys for forks, stars, issues, etc. Adding more GitHub data is as simple as finding the right key and pulling them in from the JSON fetched from the API. Pretty cool! The data in `projects.yml` is sample data that is inaccurate.

## How it works
The `projects.yml` file is generated ahead of time. In it each project is listed out with all the data included in the dashboard.html file as keys. At the time of site generation, we fetch all the data from the GitHub API no more than once per hour and inject issues, stars, and other GitHub data into the data file. If we've already grabbed the data that hour, we skip that step and use what we already have. This is to avoid API rate limits, and to keep site generation reasonably light. By the time `/dashboard` is generated, all necessary data are in YAML and read out of `{{ site.data.projects }}` for the template.