Pyperf

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* Add start/end dates and duration to the ``stats`` command
* Fix the program name: ``pyperf``, not ``pybench``!
* Fix the ``-b`` command line option of show/stats/... commands
* Fix metadata: ``load_avg_1min=0.0`` is valid!

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* Fix the ``--append`` command line option

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* Add a new ``pybench`` program, similar to ``python3 -m perf``
* Most perf CLI commands now support multiple files and support benchmark
suites.
* Add a new ``dump`` command to the perf CLI and a ``--dump`` option to
the TextRunner CLI
* ``convert`` command: add ``--indent`` and ``--remove-warmups`` options
* replace ``--json`` option with ``-o/--output``
* New metadata:

- cpu_config
- cpu_freq
- cpu_temp
- load_avg_1min

Changes:

* New :func:`add_runs` function.
* Once again, rewrite Run and Benchmark API. Benchmark name is now optional.
* New :class:`Run` class: it now stores normalized samples rather than raw
samples
* Metadata are now stored in Run, no more in Benchmark.
Benchmark.get_metadata() return metadata common to all runs.
* Metadata become typed (can have a different type than string), the
new :class:`Metadata` class formats them.

------------------------

Major change: perf now supports benchmark suites. A benchmark suite is made
of multiple benchmarks. perf commands now accepts benchmark suites as well.

New features:

* New ``convert`` command
* Add new command line options to TextRunner:

* ``--fast``, ``--rigorous``
* ``--hist``, ``--stats``
* ``--json-append``
* ``--quiet``

Changes:

* Remove ``--max-time`` option of TextRunner
* Replace ``--raw`` option with ``--worker``
* Replace ``--json`` with ``--stdout``
* Replace ``--json-file`` with ``--json``
* New ``perf convert`` command to convert or modify a benchmark suite
* Remove ``perf hist_scipy`` command, replaced with an example in the doc
* Add back "Mean +- Std dev" to the stats command
* Add get_loops() method to Benchmark
* Replace ``python3 -m perf.timeit`` (with dot) CLI with ``-m perf timeit``
(without dot)
* Add :class:`perf.BenchmarkSuite` class
* name is now mandatory: it must be a non-empty string in Benchmark
and TextRunner.
* A single JSON file can now contain multiple benchmarks
* Add a dependency to the ``six`` module
:meth:`Benchmark.add_run` now raises an exception if a sample is zero.
* Benchmark.name becomes a property and is now stored in metadata
* TextRunner now uses powers of 2, rather than powers of 10, to calibrate the
number of loops

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Changes:

* The ``hist`` command now accepts multiple files
* ``hist`` and ``hist_scipy`` commands got a new ``--bins`` option
* Replace mean with median
* Add :meth:`perf.Benchmark.median` method, remove ``Benchmark.mean()`` method
* ``Benchmark.get_metadata()`` method removed: use directly the
:attr:`perf.Benchmark.metadata` attribute
* Add ``timer`` metadata. ``python_version`` now also contains the architecture
(32 or 64 bits).

------------------------

New features:

* New ``hist`` and ``hist_scipy`` commands: display an histogram (text or
graphical mode)
* New ``stats`` command: display statistics on a benchmark result
* New ``--affinity=CPU_LIST`` command line option
* Emit a warning or an error in English if the standard deviation is larger
than 10% and/or the shortest sample is shorter than 1 ms
* Emit a warning or an error if the shortest sample took less than 1 ms
* Add ``perf_version``, ``duration`` metadata. Moreover, the ``date`` metadata
is now displayed.

API:

* The API deeply changed to minimize duplications of data and make the JSON
files more compact

Changes:

* The command line interface also changed. For example, ``perf.metadata``
command becomes ``perf metadata``.
* On Python 2, ``psutil`` optional dependency is now used for CPU affinity.
It ensures that CPU affinity is set for loop calibration too.
* On Python 2, add dependency to the backported ``statistics`` module
* ``perf.mean()`` and ``perf.stdev()`` functions have been removed: use
the ``statistics`` module (which is available on Python 2.7 and Python 3)
* New optional dependency on ``boltons`` (``boltons.statsutils``) to compute
even more statistics in the ``stats`` and ``hist_scipy`` commands