Broken links to some pages in docs

[KyrietS]

I've created this issue to track the progress of fixing broken links on some pages.

I can successfully reproduce this weird behaviour:

1. Go to https://premake.github.io/docs/Developing-Modules/
2. Links are broken, because they are referencing /docs/Developing-Modules/* instead of /docs/*
3. Use sidebar navigation and go to Adding a New Action
4. Use sidebar navigation and go back to Developing Modules
5. Links are working fine
6. Refresh the page (F5)
7. Links are broken again

I will try do debug this but at the moment I suspect that it's Docusaurus' fault.

[Jarod42]

It seems there is a difference between
https://premake.github.io/docs/Developing-Modules (working)
and
https://premake.github.io/docs/Developing-Modules/ (not working).

[KyrietS]

Similar problem has already been reported: facebook/docusaurus#2317
The solution proposed there seems to work.

So instead of this:

* [Introduction](introducing-modules)
* [Adding Unit Tests](adding-unit-tests)
* [Sharing Your Module](sharing-your-module)
* [Embedding Modules](embedding-modules)

we should always write references to other pages like this:

* [Introduction](Introducing-Modules.md)
* [Adding Unit Tests](Adding-Unit-Tests.md)
* [Sharing Your Module](Sharing-Your-Module.md)
* [Embedding Modules](Embedding-Modules.md)

^ case sensitive!

Fortunately when I was migrating reference pages I always used filenames with *.md extensions. So there aren't many pages left to fix.

In my opinion it's a bug in Docusaurus. They should fix this weird behaviour of breaking links after refresh or mark those links as broken during building process.

Fun fact: I've already advised @starkos how to create links to other pages in my migration notes 😉

When linking to another document ALWAYS use relative path with *.md extension. Docusaurus will generate valid urls, and links will also work when browsing on GitHub. Additionally, you will get a warning message when link to a markdown file can't be resolved.

I'm working on fixing this.