SFTP is more reliable than SCP when dealing with unknown sshd configurations on the server side. It also provides a convenient facility for creating remote directories, so we can remove the Windows-specific `#create_remote_directory` method.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.