[issue906] Merge branch main.

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+/misc export-ignore
+.gitattributes export-ignore
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+.uncrustify.cfg export-ignore

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+__pycache__/
+/output.sas
+/sas_plan
+/sas_plan.*
+/builds/
+/experiments/issue*/.venv/
+/experiments/issue*/data/
+/misc/.tox/
+/misc/autodoc/downward-xmlrpc.secret

CHANGES.md

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+# Release notes
+
+Fast Downward has been in development since 2003, but the current
+timed release model was not adopted until 2019. This file documents
+the changes since the first timed release, Fast Downward 19.06.
+
+For more details, check the repository history
+(<http://hg.fast-downward.org>) and the issue tracker
+(<http://issues.fast-downward.org>). Repository branches are named
+after the corresponding tracker issues.
+
+## Changes since the last release
+
+- Fix crash when using `--show-aliases` option of fast-downward.py.
+
+- Fix incorrect computation of derived predicates.
+  <http://issues.fast-downward.org/issue453>
+  Derived predicates could be evaluated incorrectly in cases where
+  there is a cyclic dependency between derived variables and the
+  derived predicate is only ever needed in negated form. This has been
+  fixed.
+
+- Integrate new pruning method `atom_centric_stubborn_sets()`
+  <http://issues.fast-downward.org/issue781>
+  We merged the code for the SoCS 2020 paper "An Atom-Centric Perspective
+  on Stubborn Sets" (https://ai.dmi.unibas.ch/papers/roeger-et-al-socs2020.pdf).
+
+- Remove deprecate aliases for linear merge strategies and the DFP merge
+  strategy: command line options merge_linear and merge_dfp are no longer
+  available. See http://www.fast-downward.org/Doc/MergeStrategy for equivalent
+  command line options to use these merge strategies.
+
+- For developers: Use global logging mechanism for all output
+  <http://issues.fast-downward.org/issue963>
+  All output of the planner is now handled by a global logging mechnism, which
+  prefaces printed lines with time and memory information. For developers, this
+  means that output is no longer passed to cout, but utils::g_log.
+
+- For developers: store enum options as enums (not ints) in Options objects.
+  <http://issues.fast-downward.org/issue962>
+
+- For developers: allow creating Timers in stopped state
+  <http://issues.fast-downward.org/issue965>
+
+## Fast Downward 19.12
+
+Released on December 20, 2019.
+
+Highlights:
+
+- Fast Downward no longer supports Python 2.7, which reaches its end
+  of support on January 1, 2020. The minimum supported Python version
+  is now 3.6.
+
+- Fast Downward now supports the SoPlex LP solver.
+
+Details:
+
+- general: raise minimum supported Python version to 3.6
+  <http://issues.fast-downward.org/issue939>
+  Fast Downward now requires Python 3.6 or newer; support for Python 2.7 and
+  Python 3.2-3.5 has been dropped. The main reason for this change is Python 2
+  reaching its end of support on January 1, 2020. See
+  https://python3statement.org/ for more background.
+
+- LP solver: add support for the solver [SoPlex](https://soplex.zib.de/)
+  <http://issues.fast-downward.org/issue752>
+  The relative performance of CPLEX and SoPlex depends on the domain and
+  configuration with each solver outperforming the other in some cases.
+  See the issue for a more detailed discussion of performance.
+
+- LP solver: add support for version 12.9 of CPLEX
+  <http://issues.fast-downward.org/issue925>
+  Older versions are still supported but we recommend using 12.9.
+  In our experiments, we saw performance differences between version
+  12.8 and 12.9, as well as between using static and dynamic linking.
+  However, on average there was no significant advantage for any
+  configuration. See the issue for details.
+
+- LP solver: update build instructions of the open solver interface
+  <http://issues.fast-downward.org/issue752>
+  <http://issues.fast-downward.org/issue925>
+  The way we recommend building OSI now links dynamically against the
+  solvers and uses zlib. If your existing OSI installation stops
+  working, try installing zlib (sudo apt install zlib1g-dev) or
+  re-install OSI (http://www.fast-downward.org/LPBuildInstructions).
+
+- merge-and-shrink: remove trivial factors
+  <http://issues.fast-downward.org/issue914>
+  When the merge-and-shrink computation terminates with several factors
+  (due to using a time limit), only keep those factors that are
+  non-trivial, i.e., which have a non-goal state or which represent a
+  non-total function.
+
+- tests: use pytest for running most tests
+  <http://issues.fast-downward.org/issue935>
+  <http://issues.fast-downward.org/issue936>
+
+- tests: test Python code with all supported Python versions using tox
+  <http://issues.fast-downward.org/issue930>
+
+- tests: adjust style of Python code as suggested by flake8 and add this style
+  check to the continuous integration test suite
+  <http://issues.fast-downward.org/issue929>
+  <http://issues.fast-downward.org/issue931>
+  <http://issues.fast-downward.org/issue934>
+
+- scripts: move Stone Soup generator scripts to separate repository at
+  https://github.com/aibasel/stonesoup.
+  <http://issues.fast-downward.org/issue932>
+
+## Fast Downward 19.06
+
+Released on June 11, 2019.
+First time-based release.