Add site.repository for the URL on Github. Close #1456
Ignore _site in jekyllrb.com deploy.
Fix docs/templates.md private gist example.

Duplicate of #1477 because we develop on the master branch.
Update history to reflect merge of #1477
Merge pull request #1463 from penibelst/add-site-repository

Add site.repository for the URL on Github. Close #1456
Update history to reflect merge of #1463
Merge pull request #1480 from mojombo/ignore-_site-in-deploy

Ignore _site in jekyllrb.com deploy.
Update history to reflect merge of #1480