Implementation Notes

• This will be done in the docs module and will be independent of ABP documentation.
• We can start with markdown first. We can merge all documents into a single Markdown file. Then we can convert this to PDF later. We can allow it to download as MD or PDF.
• Use the docs-nav.json file as the source, go to the documents one by one and create a single MD file.
• One problem: Some documents (example) have multiple options (UI and DB, mostly). For this documents, they system should place the document multiple times, each for a specific configuration. Example: The resulting single MD file should contain these titles: "TODO Application Tutorial with Single-Layer Solution (Angular, Entity Framework Core)", "TODO Application Tutorial with Single-Layer Solution (MVC / Razor Pages, MongoDB)". For this tutorial, we will have 8 copies in the resulting file with different titles (same title, but with different parathesis).
• Another problem: Some documents may not included in docs-nav.json file. They are linked inside a module and no direct way to access thought the navigation menu. As a solution, I offer to add all them to the docs-nav.json file, but with an optional
  "hidden": "true" property. So, this is a new property (default value is false, if not defines) and the docs module should check it and skip that item while rendering on the menu. So, it is a backward compatible new feature for the docs module.
• Another problem: We may have some items on the docs-nav file, but we may want to exclude them from the PDF file. For example, no need to include https://abp.io/docs/latest/kb/index . For these items, define a new optional property "ignoreOnDownload": "true" (default: false, if not defined). We can ignore these kind of documents.