text: Title: [RFC] Link checker for documentation
  Body: **Is your feature request related to a problem? Please describe.**
  Often internal links can be misspelled or external links be down.
  
  **Describe the solution you'd like**
  Implement a link checker for the documentation. The fixing of the links could still be manual.
  
  Also, we could try to incorporate it to `make all` and CI and see if it produces reliable output.
  
  **Describe alternatives you've considered**
  None.
  
  **Additional context**
  Mkdocs have a simple internal link [validation](https://www.mkdocs.org/user-guide/configuration/#validation), but maybe some third part can be used instead( or along with it) for external links.