Improve handling of internal subrepo in plugins.py.

`subs()` method print an error if returned dictionary is empty.
This commit fix it by adding a condition to ensure dictionary is not empty
else return None.

Review documentation, mainly update some links and fix grammatical mistakes.

🔖 v1.0.2 (29/04/2021)

- 📝📄 Update copyright in license content
- ✨ Improve handling of copyright in plugins.py script
- 🔥 Remove useless file from tracked tree

🔖 v1.0.2 (29/04/2021)

- 📝📄 Update copyright in license content
- ✨ Improve handling of copyright in plugins.py script
- 🔥 Remove useless file from tracked tree

🔖 v1.0.1 (29/04/2021)

- 🐛🍱 Fix wrong assets path in `docs/personal_template/create.md`
- 🐛 Update `plugins.py` to latest release

🔖 v1.0.1 (29/04/2021)

- 🐛🍱 Fix wrong assets path in `docs/personal_template/create.md`
- 🐛 Update `plugins.py` to latest release

🔖 v1.0.1 (29/04/2021)

- 🐛🍱 Fix wrong assets path in `docs/personal_template/create.md`
- 🐛 Update `plugins.py` to latest release

🔖 v1.0.0 (29/04/2021)

First initial release of MkDocs Template

- ✨ Add bunch of features:
    - `setup.sh` script to automatically install template,
    - `template` folder holding basic template files, script
      `docs/_data/plugins.py` to dynamically setup `mkdocs.yml` configuration
      and schema and template for files read by the script
- 🔧 Add bunch of configuration files:
    - Syntax and workflow configuration files such as `.editorconfig`,
      `.yamllint`, `pyproject.toml`
- 👷 Add CI which test the scripts (bash and python), build the
  documentation and deploy it
- 📝🍱 Add the documentation describing the usage of the template with needed
  assets.
- 📄 Add licenses, MIT and Beer-Ware.

🔖 v1.0.0 (29/04/2021)

First initial release of MkDocs Template

- ✨ Add bunch of features:
    - `setup.sh` script to automatically install template,
    - `template` folder holding basic template files, script
      `docs/_data/plugins.py` to dynamically setup `mkdocs.yml` configuration
      and schema and template for files read by the script
- 🔧 Add bunch of configuration files:
    - Syntax and workflow configuration files such as `.editorconfig`,
      `.yamllint`, `pyproject.toml`
- 👷 Add CI which test the scripts (bash and python), build the
  documentation and deploy it
- 📝🍱 Add the documentation describing the usage of the template with needed
  assets.
- 📄 Add licenses, MIT and Beer-Ware.

📝 Write main documentation of the usage of the template.

🔧 Update mkdocs.yml configuration and add extra variables in `docs/_data/`.

🍱 Add img assets for the documentation.

Write the main documentation of the usage of the template.
Add img corresponding to new pages.
Add extra variable needed for the documentation

Due to `last_*` being 0, versioning handling was wrong when rendering the
documentation as this create a version 0.0.0 in the file version.json.

This commit fix this issues by setting `last_*` variables to `-1` and adding a
small test to better handle versioning of the documentation.

Add copyright notice in docs/_data/vars.yaml from mkdocs_template_rdeville.