libssh2 1.9.0

This release includes the following enhancements and bugfixes:
 
 o adds ECDSA keys and host key support when using OpenSSL
 o adds ED25519 key and host key support when using OpenSSL 1.1.1
 o adds OpenSSH style key file reading
 o adds AES CTR mode support when using WinCNG
 o adds PEM passphrase protected file support for Libgcrypt and WinCNG
 o adds SHA256 hostkey fingerprint
 o adds libssh2_agent_get_identity_path() and libssh2_agent_set_identity_path()
 o adds explicit zeroing of sensitive data in memory
 o adds additional bounds checks to network buffer reads
 o adds the ability to use the server default permissions when creating sftp directories
 o adds support for building with OpenSSL no engine flag
 o adds support for building with LibreSSL
 o increased sftp packet size to 256k
 o fixed oversized packet handling in sftp
 o fixed building with OpenSSL 1.1
 o fixed a possible crash if sftp stat gets an unexpected response
 o fixed incorrect parsing of the KEX preference string value
 o fixed conditional RSA and AES-CTR support
 o fixed a small memory leak during the key exchange process
 o fixed a possible memory leak of the ssh banner string
 o fixed various small memory leaks in the backends
 o fixed possible out of bounds read when parsing public keys from the server
 o fixed possible out of bounds read when parsing invalid PEM files
 o no longer null terminates the scp remote exec command
 o now handle errors when diffie hellman key pair generation fails
 o fixed compiling on Windows with the flag STDCALL=ON
 o improved building instructions
 o improved unit tests
 
This release would not have looked like this without help, code, reports and
advice from friends like these:

  Peter Surge, Will Cosgrove, Daniel Stenberg, Alex Arslan, Alex Crichton, 
  Thomas Bleeker, Keno Fischer, Marc Hörsken, Marcel Raad, Viktor Szakats,
  Kamil Dudka, Panos, Etienne Samson, Tseng Jun, Brendan Shanks, doublex,
  Erik B, Jakob Egger, Thomas Lochmatter, alex-weaver, Adrian Moran, Zenju,
  gartens, Matthew D. Fuller, Ryan Kelley, Zhen-Huan HWANG, Orivej Desh, 
  Alexander Curtiss
  
  (29 contributors)
