Close swcarpentry/lesson-example/193

https://cran.r-project.org/doc/manuals/r-patched/R-exts.html#Specifying-URLs

Close #211

Close #217

Close #150

Close https://github.com/swcarpentry/lesson-example/issues/145.

Close #178

Close #176

Close #177

This is based on https://github.com/swcarpentry/lesson-example/pull/127/.

By doing this, when a page is heavily zoomed in (e.g. 500%) the navbar
icons stay in the same row, rather than breaking onto two different rows.

by run

~~~
$ find _includes -type f -exec sed -i "s/page.carpentry/site.carpentry/g" {} \;
$ find _layouts -type f -exec sed -i "s/page.carpentry/site.carpentry/g" {} \;
$ find _extras -type f -exec sed -i "s/page.carpentry/site.carpentry/g" {} \;
$ find _episodes -type f -exec sed -i "s/page.carpentry/site.carpentry/g" {} \;
$ find bin -type f -exec sed -i "s/page.carpentry/site.carpentry/g" {} \;
$ find assets -type f -exec sed -i "s/page.carpentry/site.carpentry/g" {} \;
~~~

Close #155

Rebased of https://github.com/swcarpentry/lesson-example/pull/116/.

Thanks to @tracyteal.

Includes @drjwbaker's description of Library Carpentry.

As suggested by @gcapes.

Related with https://github.com/swcarpentry/styles/issues/80.

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