Merge pull request #13 from smcgregor/master

Port Privly Dev School to Priv.ly
privly.js: set download page button href
privly.css: style big_download_link
download.md: prominent download button
default.html: privly.js script
download.md: open extension links in new tab
rename privly.js to site.js
site.js: add comments
move scrollspy to site.js
Merge branch 'spectralsun-highlight-download'