Adding accessibility changes from swcarpentry/styles

Adding Google Analytics code

Merge branch 'gh-pages' of https://github.com/swcarpentry/styles into gh-pages to accommodate accessibility changes

Fix display of double curlies using {% raw %}

Fix broken link to training memory lesson

accessibility fixes.

fix search meta tag.

Add label to search box and navigation arrows.

1. Checking that `index.md` has `root` set to '.'
2. Checking that `_config.yml` has `root` set to '..'

Adding link to syllabus (episodes) from setup instructions

Mention that R packages are needed to build example lesson.

1.  Adding link using `page.root`.
2.  Adding ID attribute to syllabus.

Replaces #56.

fixing name of lesson_initialize.py script in point 11

Disambiguating "guides"

Adding a footnote to the schedule that it may vary.