Add explicit #include that was failing on some platforms.

Include note on ml_flags failure on import.

Suggest change for Py_SETREF().

Add warning on Py_SETREF and Py_XSETREF. Fixes to Python 3 links.

v0.3.1rc0. Fixes #33

Merge remote-tracking branch 'origin/master'

Fix typo in HISTORY.rst

Finish preparing 0.3.0 release.

First test of release 0.3.0. build_all.sh passes.

Review edits of install.rst

Review edits of compiler_flags.rst

Review edits of watchers.rst

Review edits of pickle.rst

Review edits of context_managers.rst. Build all documentation with on…

Review edits of iterators_generators.rst

Review edits of files.rst

Review edits of logging.rst

Review edits of new_types.rst

Review edits of parsing_arguments.rst

Review edits of canonical_function.rst and exceptions.rst

Review edits of exceptions.rst

Review edits of struct_sequence.rst

WIP on struct_sequence.rst

Fix misunderstanding about PyDict_GetItemWithError() in containers_an…

Finish containers_and_refcounts.rst with a number of TODOs.

Add a todo in containers_and_refcounts.rst.

WIP on containers_and_refcounts.rst. CLion is locking up again.

Add note on the rare use of the Mapping Protocol.

Finish edit for refcount.rst

Finish edit for new_types.rst