Disable "pycontextvar" test in PyPy which (as of 7.3.4) seems to lack the C-API support for context variables.

Also fixes the control flow analysis for loop variable assignments in this case.
Closes https://github.com/cython/cython/issues/3787

Make a test cleaner for what it should test. We do not care whether (Py2) 'str' works as long as unicode strings work.

Resolve a C compiler warning in the fallback code for PyContextVar_Get() due to an invalid conditional expression that was mixing a void command with a pointer value.

Add sort of a "Related Work" section to the github readme that references and compares other Python compiler projects.

Do not install Pythran in 0.29.x on travis since it is currently incompatible and unknown when it will work again.

Closes https://github.com/cython/cython/issues/4061

A bug in distutils means that it tries to export a slightly incorrectly named PyInitU function. The fix in https://bugs.python.org/issue39432 wasn't quite right (`"_name".encode("punycode") != "name".encode("punycode")`) and thus the "unicode_imports" test is failing on Windows 3.8+ when distutils explicitly tries to export a non-existing symbol.

We now create a dummy function with that alternative name so that the export doesn't fail.

Use new PyGC_Enable() and PyGC_Disable() functions in CPython 3.10 where we need to temporarily disable the GC.

Implement "gen.gi_frame" and "coro.cr_frame" attributes on generators and coroutines that return an inspectable (although otherwise dead) frame object.

Closes https://github.com/cython/cython/issues/2306

Provide a fallback implementation for PyContextVar_Get() that always returns the default value on Py<3.7.
This is currently needed to make the inline functions compile, because it seems that we are not properly excluding unused ones.

Correct the declaration of PyContextVar_New() and add convenience functions for getting context variable values.

See https://github.com/cython/cython/issues/2281
See https://github.com/cython/cython/pulls/4088

Closes https://github.com/cython/cython/issues/2281

The utility code was generated at too late a stage, after the utility code from the pxd was merged into the pyx scope.

Fixes #1415

The utility code was generated at too late a stage, after the utility code from the pxd was merged into the pyx scope.

Fixes #1415

* Use the same fallback as for missing PEP-393 support.
* Prepare for "PyUnicode_READY()" and "PyUnicode_WCHAR_KIND" to be removed in Py3.12.
  See https://www.python.org/dev/peps/pep-0623/
* Avoid C compiler warnings about deprecated C-API functions in Py3.9+.

Closes https://github.com/cython/cython/issues/3925

* Use the same fallback as for missing PEP-393 support.
* Prepare for "PyUnicode_READY()" and "PyUnicode_WCHAR_KIND" to be removed in Py3.12.
  See https://www.python.org/dev/peps/pep-0623/
* Avoid C compiler warnings about deprecated C-API functions in Py3.9+.

Closes https://github.com/cython/cython/issues/3925