Doc: Classes: Correct links to parent/related classes

[tsubotitsch]

e.g. https://github.com/fasteiner/Notion/wiki/04_Block -> Link to notion_parent remove .md

Solution for flat structure in wiki vs. link inside file view?
https://github.com/fasteiner/Notion/wiki/04_Block
https://github.com/fasteiner/Notion/blob/main/docs/Classes/Block/04_Block.md