Add current year to copyright of workshop footer

Updated lesson_initialize

Fix CSS to use .language-X class

Advise users not to edit .md files generated from .Rmd files

secure hyperlinks to pre-empt server-side HTTPS redirects

Reorganized description of process for contributing to clarify/increase readability

Changed the keyword for emailing from 'contact' to 'email' per https://github.com/swcarpentry/styles/issues/178 and changed the description for how to use GitHub to reflect usage of the web interface.

Fix bin/lesson_initialize.py

If _extras/figures.md exists,

    $ ./bin/lesson_initialize.py

will return

    Warning: _extras/figures.md already exists.
    **Exiting without creating files.**

Close #150

Close #152.

Syntax highlight

Based on https://github.com/swcarpentry/lesson-example/pull/144/files

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

Clarified instructions for using GitHub to contribute, altered link for [issues] to direct to GitHub page on navigating issues to avoid FIXME issue with link when initializing, removed link to master repo to avoid FIXME issue with link when initializing. These suggestions were based on a pull request initially done elsewhere swcarpentry/shell-novice#639

Close #186

Adopt email instead of contact as keyword

Close #178

Replace extract_figures.py with Javacript

Demo at https://github.com/swcarpentry/lesson-example/pull/132/.

add keyboard key style

Fix concept-maps link

Close #176

Fix github-importer link

Close #177

Add "Offline" Capable

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