Pages: Jekyll to v0.5.7 + Rewrites

I have a few quick Pages updates worth noting. Jekyll has been upgraded from v0.5.4 to v0.5.7. You can find a list of changes in the history file. And, by popular demand, requests for you.github.com/some/file are now rewritten to you.github.com/some/file.html (e.g., this and that).