Documentation updates

[rm5248]

This PR does the following:

• Convert apt/xdoc documentation to markdown
• Use doxygen for site generation instead of maven
• Let CMake generate the tar.gz/zip files for releases, as well as signing them
• Recreate the important generated pages that maven generates in markdown(download, mailing list, source repository)
• Added a new documentation page with some configuration samples

[ams-tschoening]

How to enable generating a TAR etc. for releases:

How to enable generating the SITE:

[ams-tschoening]

Things look good in general to me, though I have some minor suggestions and questions.

How do you plan to handle obsolete parts of ANT, MVN etc.? With an additional PR or make it part of this or ...?

[ams-tschoening]

How do you execute that target, on the shell and with which command? Visual Studio doesn't seem to provide anything obvious in its UI, installing doesn't seem to trigger that target. Adding ALL like for Doxygen does, but that's not what you intended?

[rm5248]

At least on *nix, this creates a 'make dist' target. With Visual Studio, you need to switch to 'CMake Targets View' in the Solution Explorer. You can then run the target from there.

[ams-tschoening]

thanks, found it with a little help:

https://devblogs.microsoft.com/cppblog/cmake-support-in-visual-studio-targets-view-single-file-compilation-and-cache-generation-settings/

[rm5248]

Things look good in general to me, though I have some minor suggestions and questions.

How do you plan to handle obsolete parts of ANT, MVN etc.? With an additional PR or make it part of this or ...?

I was going to do that as a separate PR, as I was only focusing on the website building with this PR.