[netcurl] netcurl-6.1 soon to be merged into the master branch

Stable releases for netcurl v6.0 will, for now on, no longer be pushed into the master repository. A new stable/6.0 has been created for maintenance releases. Version 6.1 is quite close to get a new tag and there's not many compatibility issues left to take care of. The only bigger part that awaits for 6.1 is the complementary network module.