Documentation hosting on Github Pages (#11)

Before this PR, the only way to access the documentation was by browsing through the repository's markdown files.
Using the mkdocs framework, an alternative way was created to view documentation as a website.

This patch contains:
- Mkdocs config file `mkdocs.yml`.
- Small corrections in .md files for more correct rendering on the website.
- Custom hooks before site build to ensure .md file links remain
  accurate in both the website and repository versions of the docs.
- CI workflow to deploy the documentation site to GitHub Pages.

To check how the site looks locally, you need to:

```
make doc
```

Open documentation on http://localhost:8000/

Important:
- In the repository settings, set the Github Actions source for Github Pages.
  Settings -> Pages -> Build and deployment: "GitHub Actions"
- The documentation is deployed in the `github-pages` environment.
  You can set up rules for each environment (for example, a timer for deferred deployment)
  Settings -> Environment -> [env-name]

Co-authored-by: Vladimir Severov <hackallcode@users.noreply.github.com>

Author: hackallcode

.github/workflows/ci.yml

@@ -27,13 +27,7 @@ jobs:
       - name: "Create semantic tag"
         id: "create-tag"
         run: |
-          if [ "${{ github.ref_name == github.event.repository.default_branch }}" != "true" ]; then
-            echo "Skipping tagging because it's not the default branch"
-            exit 0
-          fi
-
-          VERSION=$(echo "${{ github.event.head_commit.message }}" \
-            | sed -nE 's/.*[Rr]elease ([0-9]+\.[0-9]+\.[0-9]+).*?/\1/p')
+          VERSION=$(git log -1 --pretty=%B | sed -nE 's/.*[Rr]elease ([0-9]+\.[0-9]+\.[0-9]+).*?/\1/p')
 
           if [ -z "${VERSION}" ]; then
             echo "No semantic version found in commit message"