* be more friendly in the deprecation of cv=3

* add hint on specifying cv

* catch all the right warnings

* fix warning issues

* add comments

* add some tests

* pep8

* ENH Pipeline can now be sliced or indexed

* Additional assertion imports for testing

* DOC Documentation and example for Pipeline slicing

* FIX put doctest lines in correct order

* DOC improve compose Pipeline docs

* Fix doctest

* Fix merge error

* DOCs improved after Alex's comments

* This is not the right place to change to LinearSVC

* missed one

* DOC add what's new

* Fix doctest

* doctest tweaks

Co-Authored-By: jnothman <joel.nothman@gmail.com>

* doctest tweaks

Co-Authored-By: jnothman <joel.nothman@gmail.com>

* doctest tweaks

Co-Authored-By: jnothman <joel.nothman@gmail.com>

* fix doctests

* Correct step name

* Update doc/whats_new/v0.21.rst

Co-Authored-By: jnothman <joel.nothman@gmail.com>

* fix LDA predict_proba() to handle binary and multi-class case

* test_lda_predict_proba non-regression test

* pep8 fix

* lda predict_proba refactoring

* Typo fix

* flake8 fix

* predict_proba check_is_fitted check

* update what's new rst file

* rename prob to decision

* include additional tests for predict_proba

* use allcose vs. assert_array_almost_equal

* fix indent

* replace len with size

* explicit computation for binary case

* fix style whats_new rst

* predict_proba new regression test

* give credit for regression test

* fix bug for eigen solution

* include all three solvers in predict_proba regression test

*  update whats_new rst file

* fix minor formatting issue

* use scipy.linalg instead of np.linalg

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