Prevent overflowing hash values for "Machines.Node" due to arbitrarily large unsigned pointer values.
Closes https://github.com/cython/cython/issues/3840

Specifically this allows public packed structs but may also allow other public declarations that require small amounts of utility code.

Add "check_size ignore" to all NumPy.pxd class declarations to silence the useless size warnings about them.
See https://github.com/numpy/numpy/pull/432#issuecomment-689846159
Also remove the useless "extern" modifiers from cdef classes declared in "extern" sections.

Closes #3680.

Python's asyncio.coroutines uses an object to tag objects as coroutine functions. We now read this object and use it to tag Cython compiled coroutines as well.

It also includes tests to make sure `asyncio.iscoroutinefunction()` works as expected.
This doesn't fix `inspect.iscouroutinefunction()` (which uses a flag that can trigger undesirable behaviour for cython functions).

Closes https://github.com/cython/cython/issues/2273

Fixes GH-2749.

Rename "GCC_DIAGNOSTIC" macro to make it Cython specific and make it available to other utility code sections.

In C++ mode, structs can contain C++ classes. Therefore structs
should have their destructors called to ensure any class
contained is also destructed.

Also, a bit more thorough about ensuring constructor is generated where necessary.

Closes GH-3226.

Change test to use only integer calculations to prevent platform specific rounding issues, while keeping a reasonable distribution of integers across the PyLong digit ranges.

Ensure that Cython exposes `PyBUF_MAX_NDIM` from Python as part of
`cpython.buffer` to allow access to developers.

Fixes GH-2749.

Rename "GCC_DIAGNOSTIC" macro to make it Cython specific and make it available to other utility code sections.

Mainly by moving it to a separate section to make it easier
to find, however also added a small amount of extra information
about some of the obvious limitations.

* Cython debugger documentation: Added link to an installation script.
* Got a new libpython.py from the cpython source distribution.
* Default language level in tests is now 3 instead of 2
* Migrated codefile from python 2 to python 3.
* Added testcase for the cy list command in cygdb.
* Temporarily removing test case that freezes gdb.
* Fixed a bug that broke several Cygdb tests.

The cython_debug/cython_debug_info_* files map the names of the C-functions generated by the Cython compiler to the names of the functions in the *.pyx source. If the function was defined using "def" (and not "cpdef" or "cdef") in the *.pyx source file, the C-function named in cython_debug/cython_debug_info_* used to be __pyx_pw_*, which is the name of the wrapper function and now it is __pyx_f_*, which is the name of the actual function. This makes some Cygdb tests pass that did not pass before.

* Better error messages: If a cygdb command raises, a traceback will be printed.
* Fixed a bug in cygdb.

The following now works:
1. Start cygdb
2. Type "cy exec" and hit enter
3. Type some other lines
4. Type "end" and hit enter.
-> These "other lines" will get executed

* Fixed a bug in cygdb: cy list now works outside of functions.
* Added print_hr_allmarkers function for easier debugging.
* Fixed a bug that broke cygdb:

cy break did not work if you put the breakpoint outside of a function if there was e.g. the following somewhere in your *.pyx file:
cdef class SomeClass():
    pass

* Added a Cygdb test for printing global variables.
* Fixing cygdb: Replaced cy print with a simple, working solution.
* If an exception in Cygdb occurs, a stacktrace will be printed.
* Fixed a bug that broke cy break -p
* Bugfix: The compiler now writes out correctly which cython linenumber and path corresponds to which c linenumber.
* Set language_level=2 in runtests.py

Fixes https://github.com/cython/cython/issues/1071

There's now a fairly wide range of valid syntax for declaring things in pyx files and it should all be supported when cimporting from them.

This reverts commit a333d6a8.

The change did not resolve the test issue in travis.

Closes https://github.com/cython/cython/issues/3775