Idea: Split setup instructions into one file per lesson

[danmichaelo]

The setup instructions makes the index.md quite long and cumbersome to work with. What do you think about extracting the setup instructions into one file per lesson? Has this been discussed before? I could make a PR, but thought it'd be a good idea to discuss first. I imagine the setup instructions in index.md could look something like this:

<h2 id="setup">Setup</h2>
...
{% include setup/shell.html %}
{% include setup/git.html %}
{% include setup/editor.html %}
{% include setup/python.html %}
{% comment %}
  {% include setup/r.html %}
  {% include setup/openrefine.html %}
  ...
{% endcomment %}

[danmichaelo]

Closing in favour of #408