v0.29.3

• update to libssh 0.9.3, see https://www.libssh.org/2019/12/10/libssh-0-9-3-and-libssh-0-8-8-security-release/
  containing also 0.9.2, see https://www.libssh.org/2019/11/07/libssh-0-9-2/