For gollum code, everything should fall under the existing MIT License.
Alternative permissive licenses (such as BSD) for 3rd party dependencies are
acceptable. For image assets in Gollum, CC BY or CC BY-SA is fine. Anything
released under a copyleft license (for example GPL, AGPL, LGPL, MPL, EPL,
etc.) is not permitted in gollum. Public domain, CC BY or CC BY-SA for code in
gollum is not permitted.