Added functionality to test multiple versions of python using tox

.gitignore

@@ -61,3 +61,9 @@ tsfresh/notebooks/data/
 # dask
 dask-worker-space
 dask-worker-space/
+
+# python version files
+.python_version
+
+# tox log files
+.tox

docs/text/how_to_contribute.rst

@@ -67,6 +67,18 @@ you have to:
     pytest
 
 
+To test changes across multiple versions of Python, run:
+
+
+.. code::
+
+    tox -r
+
+
+`tox -r` will execute tests for the Python versions specified in `setup.cfg <https://github.com/blue-yonder/tsfresh/blob/1297c8ca5bd6f8f23b4de50e3f052fb4ec1307f8/setup.cfg>`_ using the `envlist` variable. For example, if `envlist` is set to `py37, py38`, the test suite will run for Python 3.7 and 3.8 on the local development platform, assuming the binaries for those versions are available locally. The exact Python microversions (e.g. `3.7.1` vs `3.7.2`) depend on what is installed on the local development machine.
+
+A recommended way to manage multiple Python versions when testing locally is with `pyenv`, which enables organized installation and switching between versions.
+
 Documentation
 '''''''''''''
 
@@ -90,3 +102,9 @@ We use black and isort for styling. They are automatically triggered on every co
 
 
 We are looking forward to hear from you! =)
+
+
+PR Descriptions
+'''''''''''''''
+
+The PR should have a clear and descriptive title, along with a detailed description of the changes made, the problem being addressed, and any relevant tips for reviewers. An example of what this might look like is `here. <https://github.com/blue-yonder/tsfresh/pull/994#issue-1509962136>`_

setup.cfg

@@ -140,3 +140,23 @@ max-line-length = 120
 # This will be used when updating. Do not change!
 version = 3.2.3
 package = tsfresh
+
+[tox:tox]
+# Tox global conifguration options
+minversion = 4.0.0
+# Which python versions to test for
+envlist = py37, py38, py39, py310, py311
+# Don't throw an error if a specific version of python is not installed
+skip_missing_interpreters = True
+# Ensure that tox uses a virtual environment to build a source distribution
+isolated_build = True
+
+# Tox configuration options for each version of python
+[testenv]
+commands =
+    # display the python version that tests are being run on
+    python -V
+    # install package requirements before running tests
+    python -m pip install .[testing]
+    # run the tests
+    python -m pytest tests/