[WIP] Added built-in documentation

[adriengivry]

Description

The objective of this PR is to add documentation directly inside of Overload's repository, making it easy for any contributor to update it alongside PRs, as well as versioning it (e.g. the scripting API might change from one version to another, so having it alongside the code makes this easier).

A website can be statically generated from the documentation using hugo.

• Moved documentation from Wiki to new Documentation/ folder
• Added a Documentation project to premake5 to generate the documentation when building OvEditor
• Updated Menu Bar > Help to include a "Documentation" button, which either open the locally generated documentation (version-specific) if available, or the new https://doc.overloadengine.org hosted version (latest only).
• Added OpenDocumentation.bat script to start a web server and open the documentation in the default web browser (mostly for development purposes, to preview the documentation while editing).
• Updated README.md to explain the new documentation generation workflow.

To-Do

• Move tutorial/documentation images from github to local
• Setup https://doc.overloadengine.org
• Validate GitHub page deployment workflow
• Find a way to avoid duplicating hugo.toml and hugo-local.toml for online/offline builds
• Verify all new lua examples

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[adriengivry]

For versioning, we can consider:
https://discourse.gohugo.io/t/documentation-site-versioning/5898/3