some cleanup to make the repository cooler

• move some old stuff in oldstuff/, it's a kind of purgatory before potential deletion
  please give a comment about the name of this directory, I was lacking some inspiration
• rename the appveyor file as a dot file (it's supported by appveyor), it is used in any way?
• a lot of readme improvements

the move of old files would make the netradiant gitlab homepage more usable, not requiring to scroll so many useless lines before getting to readme