Add Creative Commons licenses

[wang-arthur]

• Include this in a new, formalized publication agreement (#17)
• Can we apply this retroactively, or do we need to contact every past author individually? I'm guessing we'll need to contact authors, since we don't have formal agreements in place (we shouldn't license their work without their express approval)

Wordpress Plugin

[wang-arthur]

https://wiki.creativecommons.org/wiki/Considerations_for_licensors_and_licensees