Move docs for v1 from Wiki to GitHub Pages

[ThomasPe]

I set up a static site generator using mkdocs so we can create version-specific documentation shown on GitHub Pages: https://wp-net.github.io/WordPressPCL/. All docs live inside the docs folder on master and can be configured in the mkdocs.yml file in root.

First step is to move all existing documentation from the Wiki to the new structure and then add modified versions to v2 for the next release.

[ThomasPe]

migration has been completed, we can now add the adjusted docs vor v2