I you have a github account with Jekyll-rendered pages at:
username.github.com
is it possible to use the layouts from there to also render your project pages at:
username.github.com/projectname
If so, how?
Yes, and no. You can use the layouts to render files in the projectname
path of your username.github.com repo. If, however, you put the pages into the projectname
repo, that repo will not have access to the same layouts unless you copy them in.