Escape a Win32 path which Python thinks is an escape code

[pushfoo]

Changes

• Escape the backslash before an R in a docstring
• Escape the other backslashes in the same docstring:
  • More consistent
  • Stops it from looking like a typo which someone would waste time fixing

Why

While testing #1982, I once again ran into pytest outputting noisy error messages about \R being a deprecated escape code:

$ pytest -k test_color_type================================ test session starts ================================platform linux -- Python 3.9.2, pytest-8.0.1, pluggy-1.4.0rootdir: /home/user/src/arcadeconfigfile: pyproject.tomlplugins: cov-3.0.0, mock-3.11.1collected 786 items / 768 deselected / 18 selected tests/unit/color/test_color_type.py .................. [100%]================================= warnings summary ==================================tests/unit/test_example_docstrings.py:47 /home/user/src/arcade/tests/unit/test_example_docstrings.py:47: DeprecationWarning: invalid escape sequence \R """-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html=================== 18 passed, 768 deselected, 1 warning in 2.57s ===================