Make Linux "extra dependencies" console blocks into doctests

[dhermes]

(From #179): Convert readelf -d and related blocks in docs/python/binary-extension.rst to invoke_shell()

Also: Use invoke_shell() or similar for listing the C headers (in a built ${BEZIER_INSTALL_PREFIX}/include)

---

OLDER CONTENT:

This is for the ls .../bezier/.lib and readelf boxes. The idea behind this is that we can avoid staleness in the documentation by using a doctest instead of a console block.

This mirrors similar work done for Mac OS X (85250fd) and Windows (0284717)

On a current Linux (Ubuntu 16.04), it's "impossible" to build a manylinux wheel:

$ virtualenv venv-auditwheel
$ venv-auditwheel/bin/pip install numpy
$ venv-auditwheel/bin/pip wheel . --wheel-dir UNEDITED/
$ venv-auditwheel/bin/pip install auditwheel
$ venv-auditwheel/bin/auditwheel repair UNEDITED/bezier*.whl -w EDITED/
Repairing bezier-0.5.1.dev1-cp36-cp36m-linux_x86_64.whl
usage: auditwheel [-h] [-V] [-v] command ...
auditwheel: error: cannot repair "UNEDITED/bezier-0.5.1.dev1-cp36-cp36m-linux_x86_64.whl" to "manylinux1_x86_64" ABI because of the presence of too-recent versioned symbols. You'll need to compile the wheel on an older toolchain.

However, it is possible to bypass the command line checks and just "repair" the wheel anyway:

from auditwheel.repair import repair_wheel

repair_wheel(
    '.../UNEDITED/bezier-0.5.1.dev1-cp36-cp36m-linux_x86_64.whl',
    abi='linux_x86_64',
    lib_sdir='.lib',
    out_dir='.../EDITED',
    update_tags=True,
)

However, this still won't help because the use of the newer toolchain results in different vendored in libraries:

# On Ubuntu 16.04
$ ls -1 .lib/
libgfortran-e2b67144.so.3.0.0
libquadmath-c77230e3.so.0.0.0

# vs.

# On CentOS Docker container
$ ls -1 .lib/
libgfortran-ed201abd.so.3.0.0*

and different compiled extension ELF content:

# On Ubuntu 16.04
$ readelf -d _curve_speedup.cpython-36m-x86_64-linux-gnu.so

Dynamic section at offset 0x15f1f8 contains 27 entries:
  Tag        Type                         Name/Value
 0x000000000000000f (RPATH)              Library rpath: [$ORIGIN/.lib]
 0x0000000000000001 (NEEDED)             Shared library: [libgfortran-e2b67144.so.3.0.0]
 0x0000000000000001 (NEEDED)             Shared library: [libpthread.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
...

# vs.

# On CentOS Docker container
$ readelf -d _curve_speedup.cpython-36m-x86_64-linux-gnu.so

Dynamic section at offset 0x10d000 contains 27 entries:
  Tag        Type                         Name/Value
 0x000000000000000f (RPATH)              Library rpath: [$ORIGIN/.libs]
 0x0000000000000001 (NEEDED)             Shared library: [libgfortran-ed201abd.so.3.0.0]
 0x0000000000000001 (NEEDED)             Shared library: [libpthread.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
...

[dhermes]

Also, I am dense, it's possible to use the CLI tool without failure (via the --plat flag):

$ venv-auditwheel/bin/auditwheel repair \
>   UNEDITED/bezier*.whl \
>   --wheel-dir EDITED/ \
>   --plat linux_x86_64
Repairing bezier-0.5.1.dev1-cp36-cp36m-linux_x86_64.whl
Grafting: /lib/x86_64-linux-gnu/libgcc_s.so.1 -> bezier/.libs/libgcc_s-c77f8044.so.1
Grafting: /usr/lib/x86_64-linux-gnu/libgfortran.so.3.0.0 -> bezier/.libs/libgfortran-e2b67144.so.3.0.0
Grafting: /lib/x86_64-linux-gnu/libc-2.23.so -> bezier/.libs/libc-2-4cd1a422.23.so
warning: working around a Linux kernel bug by creating a hole of 2101248 bytes in ‘bezier/.libs/libc-2-4cd1a422.23.so’
Grafting: /lib/x86_64-linux-gnu/libm-2.23.so -> bezier/.libs/libm-2-6ea08983.23.so
Grafting: /usr/lib/x86_64-linux-gnu/libquadmath.so.0.0.0 -> bezier/.libs/libquadmath-c77230e3.so.0.0.0
Grafting: /lib/x86_64-linux-gnu/libpthread-2.23.so -> bezier/.libs/libpthread-2-4b6c9076.23.so
warning: working around a Linux kernel bug by creating a hole of 2076672 bytes in ‘bezier/.libs/libpthread-2-4b6c9076.23.so’
Setting RPATH: bezier/_curve_intersection_speedup.cpython-36m-x86_64-linux-gnu.so to "$ORIGIN/.libs"
Setting RPATH: bezier/_curve_speedup.cpython-36m-x86_64-linux-gnu.so to "$ORIGIN/.libs"
Setting RPATH: bezier/_helpers_speedup.cpython-36m-x86_64-linux-gnu.so to "$ORIGIN/.libs"
Setting RPATH: bezier/_surface_speedup.cpython-36m-x86_64-linux-gnu.so to "$ORIGIN/.libs"
Previous filename tags: linux_x86_64
No filename tags change needed.
Previous WHEEL info tags: cp36-cp36m-linux_x86_64
No WHEEL info change needed.

Fixed-up wheel written to .../EDITED/bezier-0.5.1.dev1-cp36-cp36m-linux_x86_64.whl