Update docs/python/binary-extension.rst to refer to bezier.libs.

[dhermes]

See: https://circleci.com/gh/dhermes/bezier/1745.

[dhermes]

(This is quit a sad state of affairs that I don't have easy access to a physical Linux machine, though I now realize I can emulate this test environment from macOS via Docker.)

[dhermes]

OK I ran this locally and have presumably found some kind of bug:

$ unzip bezier-2020.2.4.dev1-cp38-cp38-manylinux2010_x86_64.whl 
Archive:  bezier-2020.2.4.dev1-cp38-cp38-manylinux2010_x86_64.whl
  inflating: bezier-2020.2.4.dev1.dist-info/top_level.txt  
...
  inflating: bezier/hazmat/helpers.py  
  inflating: bezier.libs/libbezier-28a97ca3.so.2020.2.3  
  inflating: bezier.libs/libz-eb09ad1d.so.1.2.3  
  inflating: bezier.libs/libquadmath-2d0c479f.so.0.0.0  
  inflating: bezier.libs/libgfortran-2e0d59d6.so.5.0.0 

and from within the dhermes/bezier:latest container

root@892578e06ae2:/var/code/bezier/scripts/manylinux/fixed_wheels# readelf -d bezier/_speedup.cpython-38-x86_64-linux-gnu.so 

Dynamic section at offset 0x43e000 contains 27 entries:
  Tag        Type                         Name/Value
 0x000000000000000f (RPATH)              Library rpath: [$ORIGIN/../bezier.libs]
 0x0000000000000001 (NEEDED)             Shared library: [libbezier-28a97ca3.so.2020.2.3]
 0x0000000000000001 (NEEDED)             Shared library: [libpthread.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
...

[dhermes]

Looking at a fresh install of auditwheel, the versions installed are

auditwheel==3.1.0 (released January 29, 2020)
pyelftools==0.26 (released December 5, 2019)
wheel==0.34.1 (released January 30, 2020)

and don't SEEM like they would be cause for a change from bezier/.libs to bezier.libs. (Given that this builds passed at points in the month of February.)

[dhermes]

OK I was WRONG (big surprise). From the auditwheel release notes (https://github.com/pypa/auditwheel/releases/tag/3.1.0) there was a big change (pypa/auditwheel#90) to use ${SITE_PACKAGES}/bezier.libs instead of ${SITE_PACKAGES}/bezier/.libs.