fixing issue#225(deprecation...) by:
1,_config.yml; change "pygments: true" to "highlighter: pygments"
2,rss.xml&atom.xml; change "Layout: nil" to "Layout: null"
Merge pull request #226 from PetersonLian/master

fixing issue#225(deprecation warning)
Merge remote-tracking branch 'remotes/upstream/master'