Asyncssh

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* Updated unit tests to run properly in environments where OpenSSH
and OpenSSL are not installed.

* Updated a process unit test to not depend on the system's default
file encoding being UTF-8.

* Updated Mac TravisCI builds to use Xcode 8.1.

* Cleaned up some wording in the documentation.

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* Fixed an issue with preserving file access times in SFTP, and update
the unit tests to more accurate detect this kind of failure.

* Fixed some markup errors in the documentation.

* Fixed a small error in the change log for release 1.7.0 regarding
the newly added Diffie Hellman key exchange algorithms.

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* Fix an error that prevented the docs from building.

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* Added support for group 14, 16, and 18 Diffie Hellman key exchange
algorithms which use SHA-256 and SHA-512.

* Added support for using SHA-256 and SHA-512 based signature algorithms
for RSA keys and support for OpenSSH extension negotiation to advertise
these signature algorithms.

* Added new load_keypairs and load_public_keys API functions which
support explicitly loading keys using the same syntax that was
previously available for specifying client_keys, authorized_client_keys,
and server_host_keys arguments when creating SSH clients and servers.

* Enhanced the SSH agent client to support adding and removing keys
and certificates (including support for constraints) and locking and
unlocking the agent. Support has also been added for adding and
removing smart card keys in the agent.

* Added support for getting and setting a comment value when generating
keys and certificates, and decoding and encoding this comment when
importing and exporting keys that support it. Currently, this is
available for OpenSSH format private keys and OpenSSH and RFC 4716
format public keys. These comment values are also passed on to the
SSH agent when keys are added to it.

* Fixed a bug in the generation of ECDSA certificates that showed up
when trying to use the nistp384 or nistp521 curves.

* Updated unit tests to use the new key and certificate generation
functions, eliminating the dependency on the ssh-keygen program.

* Updated unit tests to use the new SSH agent support when adding keys
to the SSH agent, eliminating the dependency on the ssh-add program.

* Incorporated a fix from Vincent Bernat for an issue with launching
ssh-agent on some systems during unit testing.

* Fixed some typos in the documentation found by Jakub Wilk.

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* Added generate_user_certificate() and generate_host_certificate() methods
to SSHKey class to generate SSH certificates, and export_certificate()
and write_certificate() methods on SSHCertificate class to export
certificates for use in other tools.

* Improved editor unit tests to eliminate timing dependency.

* Cleaned up a few minor documentation issues.

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* Added generate_private_key() function to create new DSA, RSA, ECDSA, or
Ed25519 private keys which can be used as SSH user and host keys.

* Removed an unintended dependency in the SSHLineEditor on session objects
keep a private member which referenced the corresponding channel.

* Fixed a race condition in SFTP unit tests.

* Updated dependencies to require version 1.5 of the cryptography module
and started to take advantage of the new one-shot sign and verify
APIs it now supports.

* Clarified the documentation of the default return value of eof_received().

* Added new multi-user client and server examples, showing a single
process opening multiple SSH connections in parallel.

* Updated development status and Python versions listed in setup.py.