Cmany

* hide experimental `create_proj` command from the help list
* gitter community: https://gitter.im/cmany_/community

* require at least python 3.6
* add support for Visual Studio 2019
* fix the location of installed data files (mostly the help files, but this
prevented cmany from running under several scenarios, eg under some ubuntu
releases)
* make sure `--continue` still raises an exception at the end
* add support for calling cmany from an existing build directory
* other bug fixes

(first release)