Switch to Jekyll, modernize look

Significant differences:
* Single-page site
* Generated/templated by Jekyll (instead of custom scheme template engine)
* No file sizes on the example downloads.  If we decide we need to add these back in the future, it shouldn't be hard with a jekyll "tag" plugin.
* Linked to the license on choosealicense.com (as well as including it verbatim)
* Used syntax highlighting on bash code block

To see the changes for yourself, you can clone the repository, then:
```
bundle install
jekyll serve
```

Jekyll generates the static site into _site (you can use `jekyll build` to just generate it)