Closes #2643.

PyNumber_MatrixMultiply() and PyNumber_InPlaceMatrixMultiply() were
missing from number.pxd.

The comments are taken from the C API documentation
(https://docs.python.org/3.8/c-api/number.html).

Fixes "Make it a bit less likely that the Python version of cython.cast() does something unexpected/wrong."

Strings werren't static for the limited API so had to be set at module init rather than compile time.

* Fixed issue where fused functions didn't register as cyfunctions

Issue https://github.com/cython/cython/issues/3384

This happened where Cython was using a shared API because the
CyFunction type imported from the shared api wasn't the same as
used to initialize the fused function tp_base.

* Fixed issue where fused functions didn't register as cyfunctions

Issue https://github.com/cython/cython/issues/3384

This happened where Cython was using a shared API because the
CyFunction type imported from the shared api wasn't the same as
used to initialize the fused function tp_base.

Default arguments are now copied when the bound fused function is created.

Default arguments are now copied when the bound fused function is created.

1. DefNode.has_fused_arguments was set too early (before
locals/annotations) were evalutated, so function was not treated
as fused.
2. When re-evaluating the specializations of the fused function
it was treated as a redefinition because the locals/annotation was
reapplied over the specialized type.
3. Including annotation as string (required changes to
StringNode.analyse_as_type), and extra tests for fused type defined
as cython.fused_type in the Py file

Closes #3331.

Closes #1427 

Closes #3331.

* Cleanup of string initialization code for limited API

Now appears in a few large blocks rather than

```
 # if CYTHON_LIMITED_API
   individual string line
 # endif
```

* Fixed issue with some unicode strings, e.g.

```
# cython: language_level=3str, binding=True

def non_ascii_str():
    s = 'ø\x20\u0020'
    assert isinstance(s, str)
    return s
```

"@subsitute: tempita" tag ensures that they are loaded in tempita utility code class

Use correct "Py_mp_subscript" type slot for getitem() method instead of "Py_mp_ass_subscript" (which is for assignments).

Fix "unused" C compiler warning for "__pyx_FusedFunction_mapping_methods" when using the limited C-API.

* omp declare privates on outer loop, since inner loops are not 'omp parallel for'ified

They'd generate two calls - one exception checked and one not

They'd generate two calls - one exception checked and one not

Avoid deprecation warning in Cython-Inline by setting the default language level to "3str" if none is provided.

* Add more limited api support
* Fix Fused Functions
* Fixed profile
* Use PyModule_GetDict
* Simplify __Pyx_Globals
* Address issues in CommonStructures
* ifdef guard CyFunction and FusedFunction

See #2686.

Close #2686.