Fix typos discovered by codespell

[cclauss]

https://pypi.org/project/codespell

% codespell

./doc/changelog.rst:91: differenly ==> differently
./doc/changelog.rst:161: Feld ==> Field
./doc/api.rst:682: aggreggated ==> aggregated
./doc/system.rst:313: tickness ==> thickness
./doc/index.rst:7: Documenation ==> Documentation
./pyperf/_runner.py:72: approximatively ==> approximately
./pyperf/_runner.py:88: suprises ==> surprises
./pyperf/_runner.py:694: benchs ==> benches
./pyperf/_runner.py:705: benchs ==> benches
./pyperf/_runner.py:726: benchs ==> benches
./pyperf/_runner.py:726: benchs ==> benches
./pyperf/_worker.py:291: metatadata ==> metadata
./pyperf/__main__.py:709: benchs ==> benches
./pyperf/__main__.py:712: benchs ==> benches
./pyperf/__main__.py:713: benchs ==> benches
./pyperf/__main__.py:715: benchs ==> benches
./pyperf/_system.py:387: paramaters ==> parameters
./pyperf/tests/test_metadata.py:166: unexpect ==> unexpected
./pyperf/tests/test_metadata.py:199: unexpect ==> unexpected
./pyperf/tests/test_metadata.py:217: unexpect ==> unexpected

[vstinner]

LGTM, thanks