Clean up ruby script and allow authenticated github-api requests

[notZaki]

This PR addresses some of the lingering issues from #23
Although this won't change anything visual with the website, a preview is nonetheless generated here.

1. Fixed bug with bitbucket repositories having the exact time of day rather than a truncated date
   • I forgot to truncate the date/time previously
2. Moved the ruby script from _plugins to _data.
   • The script will no longer run when the site is built, rather it must be executed manually since that was the preferred workflow. This also avoids the looping issue with jekyll serve.
   • Instead of jekyll build, the script should now be executed by:

   cd path/to/_data
   ruby update.rb
   

   • In a sense, this is now not that different from how the matlab version is used
3. Allow authenticated github api requests.
   • The old script only used unauthenticated requests which are limited to 60 requests/hour. This is not a problem right now since only 18 packages currently use github, but it could become a problem in the future.
   • To make authenticated requests, the script should be run by:

   ruby update.rb "github_username" "password"
   

   • If the script is called without a username/password, then unauthenticated requests will be used by default
   • Authenticated requests are limited to 5000 requests/hour. Maybe one day we'll have 5000 github packages in packages.json and this too will become a problem. 🚀

[dgallichan]

Looks great - thanks!