Add changelog fragments

Signed-off-by: Jakub Jelen <jjelen@redhat.com>

Author: Jakuje

docs/changelog-fragments/597.bugfix.rst

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+Fixed log level mapping to cover whole libssh range -- by :user:`Jakuje`.
+
+Previously, it was not possible to set most verbose libssh log level
+``SSH_LOG_TRACE`` to get most verbose log messages useful for debugging
+connection issues. To set pylibssh session verbosity to this level, you
+can use the following snippet:
+
+    from pylibsshext.logging import ANSIBLE_PYLIBSSH_TRACE
+
+    # Initializes the new TRACE log level in python logging system
+    ssh_session = Session()
+
+    eh = logging.StreamHandler()
+    eh.setLevel(logging.ERROR)
+
+    dh = logging.FileHandler('ansible-libssh-errors.log')
+    dh.setLevel(ANSIBLE_PYLIBSSH_TRACE)
+
+    logging.getLogger('ansible-pylibssh').addHandler(eh)
+    logging.getLogger('ansible-pylibssh').addHandler(dh)
+
+    ssh_session.set_log_level(ANSIBLE_PYLIBSSH_TRACE)
+    ssh_session.connect(...)
+
+This is based on :external+python:std:ref:`logging-cookbook` and
+:external+python:std:ref:`logging-howto`.

docs/changelog-fragments/597.feature.rst

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+Made libssh use the Python :py:mod:`logging` system -- by :user:`Jakuje`.
+
+Previously, the logging was done by underlying C-code to stderr instead,
+which caused inconsistent behavior.
+
+The default log level is now set to ``ANSIBLE_PYLIBSSH_TRACE``
+and donstream loggers are able to trim the verbosity down.
+If you need a performance, you can avoid logging on the libssh
+side at source by setting lower logging value, for example:
+
+```
+ssh_session.set_log_level(ANSIBLE_PYLIBSSH_NOLOG)
+```