More adventure pointer docs

[kezz]

It would be nice to split pointer docs into it's own page(s) with the following aspects:

• [ ] Usage of the API
• [ ] Standard, Adventure-provided pointers
• [ ] Community additions (if any, open for additions for platforms/etc) - is this even something we should encourage?

Migrated from https://github.com/KyoriPowered/adventure-docs/issues/87