Compare mlxtend to GI mlxtend

[pep8speaks]

Hello @sonjaoffwood! Thanks for opening this PR.

• In the file mlxtend/feature_selection/sequential_feature_selector.py:

Line 371:17: W503 line break before binary operator Line 516:49: E126 continuation line over-indented for hanging indent Line 772:50: W292 no newline at end of file

• In the file setup.py:

Line 5:11: E126 continuation line over-indented for hanging indent Line 11:8: E126 continuation line over-indented for hanging indent Line 12:21: E261 at least two spaces before inline comment Line 12:60: W291 trailing whitespace Line 18:8: E126 continuation line over-indented for hanging indent Line 19:24: E261 at least two spaces before inline comment Line 19:89: E501 line too long (107 > 88 characters) Line 19:108: W291 trailing whitespace Line 38:8: W292 no newline at end of file

Do see the Hitchhiker's guide to code style