Add support for Python 3.8.

[dhermes]

No description provided.

[dhermes]

Relevant for removal of m (i.e. 38m -> 38 in .so files): https://bugs.python.org/issue36707

On macOS:

>>> distutils.sysconfig.get_config_var("EXT_SUFFIX")
'.cpython-37m-darwin.so'
>>> distutils.sysconfig.get_config_var("EXT_SUFFIX")
'.cpython-38-darwin.so'

[dhermes]

As part of this process I tried many pairs of numpy and scipy versions in PyPy:

scipy | numpy  | success
------+--------+--------
1.4.1 | 1.18.1 |    N
1.4.0 | 1.15.0 |    N
1.4.1 | 1.15.0 |    N
1.4.1 | 1.17.5 |    N
1.3.3 | 1.15.0 |    Y
1.3.3 | 1.17.5 |    Y
1.3.3 | 1.18.1 |    Y

This seems to contradict the SciPy 1.3.0 release notes

For running on PyPy, PyPy3 6.0+ and NumPy 1.15.0 are required.

and the 1.4.0 release notes

For running on PyPy, PyPy3 6.0+ and NumPy 1.15.0 are required.

Every time there was an error it was of the form

...
  ERROR: Failed building wheel for scipy
  Running setup.py clean for scipy
  ERROR: Command errored out with exit status 1:
   command: /pypy3-env/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-wheel-b1wdrah7/scipy/setup.py'"'"'; __file__='"'"'/tmp/pip-wheel-b1wdrah7/scipy/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' clean --all
       cwd: /tmp/pip-wheel-b1wdrah7/scipy
  Complete output (11 lines):
  /pypy3-env/lib-python/3/importlib/_bootstrap.py:219: UserWarning: builtins.type size changed, may indicate binary incompatibility. Expected 872, got 416
    return f(*args, **kwds)
...

---

UPDATE: One suggested fix for this issue is to just ignore the warning. The pypy-fix-cython-warning package on PyPI is written for Python 2, but for Python 3 we can do the same thing

echo "import warnings; warnings.filterwarnings('ignore', 'builtins.type size changed, may indicate binary incompatibility. Expected .*, got .*')" \
  > .../site-packages/pypy-fix-cython-warning.pth

but I haven't (yet) been able to get this work.