Fix #307

* Add `index page` section to documentation

The current documentation does not describe how to create a index page.
I initially found this confusing, because I expected an index page to be
a **page** rather than a section.  Thus, I tried to access the page
content with `{{ page.content }}` and was very frustrated when I could
not.

This addition clarifies that the index page is **always** a section,
even if it does not have any sub-pages.  This should also help people
who intend to use Gutenberg to build stand-alone webpages, rather than
blogs.

Add details to the templates/RSS page to clarify that the `rss.xml`
page is only generated if the `generate_rss = true` variable is set
in the site's `config.toml` page.  This information is already present
in other parts of the documentation, but is not present in the RSS page,
which could be confusing.

Closes #257

Fix #197

And fix bug with taxonomies urls

* Added inital trailing_slash impl

* Added simple test

* Updated docs website to use trailing_slash option

* Updated documentation to reflect new trailing_slash option

* Added combined cachebust and trailing_slash test

Close #167

* Finishing up site

* Make site a bit responsive

* Fix menu responsiveness

* Remove Fira Sans and revamp a bit text

* Update list of syntax and change output of syntax

* Add Rust mention

* Some doc tweaks

* Correct capitalization for GitHub

Correct capitalization for GitHub

* Some CSS tweaks

* More css tweaks + favicon

* Add link to my site

And some tweaks as I write the docs