Fix doc links (#884) (#886)

* Fix doc links (#884)

- move `/docs` to `/help`
- remove dates from doc names
- move docs to sub-directories and rename to index.md so we get nice
  urls (e.g. `help/example` rather than `help/example.html`.
- use `wget --spider` to detect and fix broken links.
- fix search rendering. Note: dark mode does not play nicely with the
  GCSE input box[1]

[1]: https://support.google.com/programmable-search/

* Update doc inputs for test generation

- include all doc *.md files in tests
- name doc tests using directory name if file name is
  `index.*`.

* Fix doc links: apply review comment

Author: dtchepak

docs/docs/2019-01-01-search.md

@@ -3,8 +3,8 @@ title: Docs and getting help
 permalink: /help.html
 ---
 
-<p>Read <a href="/docs/2010-01-01-getting-started.html">Getting started</a> for a quick tour of NSubstitute.</p>
+<p>Read <a href="/help/getting-started">Getting started</a> for a quick tour of NSubstitute.</p>
 
-<p>For more in depth information start with <a href="/docs/2010-01-02-creating-a-substitute.html">Creating a substitute</a>.</p>
+<p>For more in depth information start with <a href="/help/creating-a-substitute">Creating a substitute</a>.</p>
 
 <p>If you can't find the answer you're looking for, or if you have feature requests or feedback on NSubstitute, please <a href="https://github.com/nsubstitute/NSubstitute/issues">raise an issue</a> on our project site. All questions are welcome via our project site, but for "how-to"-style questions you can also try <a href="https://stackoverflow.com/tags/nsubstitute">StackOverflow with the [nsubstitute] tag</a>, which often leads to very good answers from the larger programming community. StackOverflow is especially useful if your question also relates to other libraries that our team may not be as familiar with (e.g. NSubstitute with Entity Framework).</p>