Doc improvements

[rasbt]

Description

Improvements to the docs, including links to the User Guides in the API docs

Related issues or pull requests

Addresses #364 (the online version of the docs will be updated upon the next mlxtend release)

Pull Request Checklist

• Added a note about the modification or contribution to the ./docs/sources/CHANGELOG.md file (if applicable)
• Added appropriate unit test functions in the ./mlxtend/*/tests directories (if applicable)
• Modify documentation in the corresponding Jupyter Notebook under mlxtend/docs/sources/ (if applicable)
• Ran nosetests ./mlxtend -sv and make sure that all unit tests pass (for small modifications, it might be sufficient to only run the specific test file, e.g., nosetests ./mlxtend/classifier/tests/test_stacking_cv_classifier.py -sv)
• Checked for style issues by running flake8 ./mlxtend

[pep8speaks]

Hello @rasbt! Thanks for submitting the PR.

• In the file mlxtend/classifier/softmax_regression.py, following are the PEP8 issues :

Line 19:80: E501 line too long (80 > 79 characters)

• In the file mlxtend/feature_selection/sequential_feature_selector.py, following are the PEP8 issues :

Line 410:80: E501 line too long (84 > 79 characters)
Line 422:80: E501 line too long (81 > 79 characters)

• In the file mlxtend/frequent_patterns/association_rules.py, following are the PEP8 issues :

Line 35:80: E501 line too long (80 > 79 characters)
Line 36:80: E501 line too long (81 > 79 characters)

• In the file mlxtend/regressor/stacking_regression.py, following are the PEP8 issues :

Line 61:80: E501 line too long (80 > 79 characters)

[coveralls]

Coverage increased (+0.02%) to 91.891% when pulling 04be1dd on doc-improvements into 41a5f99 on master.