Includes @drjwbaker's description of Library Carpentry.

Jekyll doesn't export the _episodes_rmd so we need to flag the files.
Each Rmd file must have in the YAML header

    source: Rmd

https://github.com/swcarpentry/lesson-example/pull/104#issuecomment-283310978

Add label to search box and navigation arrows.

1.  Use site.root for root path if set, otherwise use site.github.url.
2.  Display extra files for workshop-template repo as well as for lessons.