Closes #1603.

Rebased 1bb26b96 for cython 0.29.x,
and made conditional to Python 3.  This does not solve the original staticmethod problem
in Python 2 but it does resolve classmethod problems in Python 3.9.  Therefore, it unbreaks
other packages on Python 3.9, improves overall state for Python 3 and does not introduce
regressions in Python 2.

This is a backwards incompatible change that enables Python semantics for special methods by default, while the directive allows users to opt out of it and go back to the previous C-ish Cython semantics.

See https://github.com/cython/cython/issues/2056

Re-add "c_api_binop_methods" directive for backwards compatibility after reverting https://github.com/cython/cython/pull/3633 and force it to "False".
Closes #3688.

This reverts commit e6a81240.

This reverts commit d849fb23.

This reverts commit bcb93877.

This reverts commit 02bb311d.

This reverts commit 66773260.

Closes https://github.com/cython/cython/pull/3677

Allow selecting specific doctests in test modules with "-k pattern", instead of always running all tests.

… and enforce them with pycodestyle.

Closes https://github.com/cython/cython/issues/3674

Allow selecting specific doctests in test modules with "-k pattern", instead of always running all tests.

Check for exceptions also when @returns() is used, not only for "->" return type annotations. (GH-3664)

When you use Python type annotations, it would be weird if you lost Python exception propagation semantics along the way, just by compiling the code. So the default behaviour is "except? -1" here for C integer types.

Arguably, this would also be a better default for the decorator case.

See https://github.com/cython/cython/issues/3625#issuecomment-631931675