Allow version 2.1 to use linenos, start and mark in code block

This is actually a hack getting from version 2.5's plugins
I just make the related plugins to get work in 2.1, then apply the default themes in 2.5 in this 2.1 branch
Merge branch '2.1-code-start-mark' of https://github.com/benedict-chan/octopress into update-code-blocks