Pyperf

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

* Fix metadata when NOHZ is not used: when /sys/devices/system/cpu/nohz_full
contains `` (null)\n``

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

* Fix metadata when there is no isolated CPU
* Fix collecting metadata when /sys/devices/system/cpu/nohz_full doesn't exist

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

* Add :meth:`Benchmark.get_unit` method
* Add :meth:`BenchmarkSuite.get_metadata` method
* metadata: add ``nohz_full`` and ``isolated`` to ``cpu_config``
* add ``--affinity`` option to the ``metadata`` command
* ``convert``: fix ``--remove-all-metadata``, keep the unit
* metadata: fix regex to get the Mercurial revision for ``python_version``,
support also locally modified source code (revision ending with "+")

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

* Worker child processes are now run in a fresh environment: environment
variables are removed, to enhance reproducibility.
* Add ``--inherit-environ`` command line argument.
* metadata: add ``python_cflags``, fix ``python_version`` for PyPy and
add also the Mercurial version into ``python_version`` (if available)

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

* Reintroduce TextRunner._spawn_worker_suite() as a temporary workaround
to fix the pybench benchmark of the performance module.

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

Tracking memory usage now works correctly on Linux and Windows. The calibration
is now done in the first worker process.

* ``--tracemalloc`` and ``--track-memory`` now use the memory peak as the
unique sample for the run.
* Rewrite code to track memory usage on Windows. Add
``mem_peak_pagefile_usage`` metadata. The ``win32api`` module is no more
needed, the code now uses the ``ctypes`` module.
* ``convert``: add ``--remove-all-metadata`` and ``--update-metadata`` commands
* Add ``unit`` metadata: ``byte``, ``integer`` or ``second``.
* Run samples can now be integer (not only float).
* Don't round samples to 1 nanosecond anymore: with a large number of loops
(ex: 2^24), rounding reduces the accuracy.
* The benchmark calibration is now done by the first worker process