Flake8 fixes

[volcan01010]

Description

This merge request makes a number of mainly cosmetic changes to the pygeodiff directory to fix errors and warnings raised by the flake8 linting software. This removes ugly warning underlines in IDEs that report on flake8.

The fixes are:

• Fix module import related errors by explicitly defining __all__ and replacing import * syntax.
• Fix line length errors by adding .flake8 config with max-line-length of 100, shortening some lines and using # noqa where they can't be shortened.
• Fix invalid escape sequence errors in docstrings by using reST format parameter definitions e.g. :param input_file:.

To test

The result of the fixes can be seen by running flake8 pygeodiff in the project root directory in both the main and flake8-fixes branches.

The remaining errors in the flake8-fixes branch are not cosmetic, so have been left.

$ flake8 pygeodiff
pygeodiff/tests/test_skip_tables.py:22:9: F841 local variable 'modified_points' is assigned to but never used
pygeodiff/tests/test_skip_tables.py:65:9: F841 local variable 'modified_points' is assigned to but never used
pygeodiff/tests/testutils.py:69:5: E722 do not use bare 'except'
pygeodiff/tests/testutils.py:139:20: F821 undefined name 'find_diff'

[dvdkon]

Looks good to me, thanks!