[Test] Isolate test data from code

[isdanni]

For test data such as X_phys and Y_phys in test files like test_Grassmann.py, a good practice would be put test data in a separate file(for example, tests/data/Grassmann.txt) and load it during the test, this way it's easier to manage all the tests. You can also reuse all the test data if needed.

When running pytest using Python 3, I got the following deprecation warnings, which seem to be caused by a few test data formatting. Reading test coordinates from .txt will give you the same error when reading the input, which can help you debug where the issue is.(lint would also be helpful)

====================================== warnings summary ======================================
../venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/Grassmann.py:56
../venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/Grassmann.py:56
  /home/user/Documents/code/venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/Grassmann.py:56: DeprecationWarning: invalid escape sequence \D

../venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/Grassmann.py:70
../venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/Grassmann.py:70
  /home/user/Documents/code/venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/Grassmann.py:70: DeprecationWarning: invalid escape sequence \D

../venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/SPD.py:103
../venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/SPD.py:103
  /home/user/Documents/code/venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/SPD.py:103: DeprecationWarning: invalid escape sequence \i

../venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/SPD.py:119
../venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/SPD.py:119
  /home/user/Documents/code/venv/lib/python3.8/site-packages/g2aero-0.1.1-py3.8.egg/g2aero/SPD.py:119: DeprecationWarning: invalid escape sequence \D

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
========================= 14 passed, 8 warnings in 170.73s (0:02:50) =========================

[isdanni]

linking openjournals/joss-reviews#5408 for tracking review progress.

[olgadoronina]

Thanks for the recommendation, we moved the data used for testing to separate files, see commit d10114a