v9.0.0

• Add support for Putty private key files
• Add getDirectory method
• Add onChannel support to execCommand
• Rename options.options in execCommand to be options.execOptions
• Rename options.sftpOptions to options.transferOptions in putFiles
• Add withSFTP and withShell methods
• Connection timed out error is now an instance of SSHError
• Invalid argument errors are now AssertionError instances
• onKeyboardInteractive default will only be set if a config.password is provided