Update documentation and migrate to https://www.obsidian-custom-sort.info

[SebastianMC]

Recent major and minor releases and discussions included features like:

• integration with obsidian-icon-folder plugin
• clarifying the usage of an experimental feature of hiding items in File Explorer
• explaining the commands built-in into the plugin, yet not documented
• additional sorting symbols for ASCII and unicode words
• some more items like that
• support for multi-level sorting
• TODO: scan recent PRs and code updates (e.g. Feature Request: Add option to pin folder notes #79 or Feature: integration with the new core plugin 'Bookmarks' - incl. its drag & drop to allow config-less custom sorting #74)

I could do a major update of the documentation:

1. Move the content of the advanced-README.md to manual.md, leaving the former as an empty placeholer with redirection to manual.md
2. Adding new sections in manual.md with the missing items (copy & paste parts of comments from closed issues and discussions)
3. Updating the ToC

This would be mostly a manual work, not requiring a fresh head, yet a major milestone towards a good quality documentation

• bookmarks integration, videos and technical documentation

• move the advanced documentation to wiki, split in sections, add a ToC, etc.

[SebastianMC]

Started moving the documentation files from main repo to wiki