Easily compile and load packages to personal webppl.org

[mhtess]

Here's the story: I'd like to host a version of webppl.org on my webpage (e.g., personal webpage; github pages), and I'd like to include certain webppl packages on these sites. For instance, I'm teaching a class that uses a custom webppl package that students get accustomed to using and I'd like for them to be able to go to this site and test out new models.

Currently, this is possible, @hawkrobe did it here (try probability(5, Binomial({n:10, p:0.5}))), but it's not particularly easy to add things to the package without having to rebuild the entire site.