CYTHON_CACHE_DIR should also set the compiler cache

This fixes #1399.

This fixes #1393.

so far only the inline cache looked at that environment variable

Use dict versioning in Py3.6+ to reduce the overhead of checking for the "C-line in tracebacks" runtime option.

Closes #1771.

Bug fix for boolean return using statement with internal commas.

Avoid uninitialised C variable (and thus potentially undefined behaviour), even if it's not actually being used in that case.

Improve libcpp.unordered_map API

Add zip_safe=False to userguide setup.py

Misc. typos

Closes #2194.

Closes #2193.

This adds notes in the documentation to include zip_safe=False when
using setuptools instead of distutils for setup.py.

Because cimport will not load pxd definitions from a zipped egg file and
the default format when installing from a source package using
setuptools and "python setup.py install" is to create a zipped egg,
including this option will guard against this error when people install
this way.

Found via `codespell -q 3`

Closes #2134.

Added %%cython options.