Adjust permalink approach

[keunes]

Short description: Replace page-level permalink definitions with global 'pretty' permalink.

URL: review all MD files

More info:
Add to _config.yml, move existing permalink definition to documentation collection:

permalink: pretty

#112 (comment)

[ByteHamster]

I hope that this does not break existing links. If it does, I would prefer to keep it as it is.

[keunes]

We'll have to see when testing, but the idea is that the resulting links are the same as current :)