Pull Request carpentries/styles#330
Closes carpentries/styles#343

1. Fix the script so that all figures are displayed.
2. Add image numbers.
3. Don't add headers for episodes without images.
4. Add horizontal rulers to better separate adjacent images.
   Don't add a ruler after the last image in the episode.
5. Add empty lines to `figures.md` to improve code readability.
6. Use classes for styling text and figures

Close carpentries/styles#325

CODE_OF_CONDUCT.md is already at the root of the repository.

* Add 'cp' (Carpentry) as a lesson type (for instructor training)
* Explain lesson type abbreviations (swc, dc, lc, cp)
* Emphasize the fact that there is no need to edit "repository" variable in front matter

Closes swcarpentry/styles#283

`site.email` is used as:

_includes/lesson_footer.html:	        <a href="mailto:{{ site.email }}">Contact</a>
_includes/workshop_footer.html:	<a href="mailto:{{ site.email }}">Contact</a>

Therefore, it does not make sense to have `mailto` in the `email` itself.

See https://help.github.com/articles/about-community-profiles-for-public-repositories/.

Port of https://github.com/swcarpentry/r-novice-inflammation/commit/9da857efb16d7351127f2d5c46fc0af660654506.

Close swcarpentry/styles#274

This is a revamp of swcarpentry/styles#248.

Thanks to Andy Boughton.