Replacing `ldd` output with `elf-inspector`

As proposed by @pombredanne in https://github.com/stefan6419846/license_tools/commit/71cea6ce12b1f444fce1a8eb09a8c834e75c3986#r136933876, I just had a deeper look at `elf-inspector` to replace plain `ldd` calls. I have to admit that I am no ELF expert.

I used two examples to check how both approaches behave in comparison:

1. `/usr/bin/bc`:

```
$ ldd /usr/bin/bc
linux-vdso.so.1 (0x00007ffd973cb000)
libreadline.so.7 => /lib64/libreadline.so.7 (0x00007fc22c800000)
libc.so.6 => /lib64/libc.so.6 (0x00007fc22c609000)
libtinfo.so.6 => /lib64/libtinfo.so.6 (0x00007fc22ceb3000)
/lib64/ld-linux-x86-64.so.2 (0x00007fc22cf0b000)
$ python -c "from elf_inspector import elf; print(list(elf.get_elf_dependencies(location='/usr/bin/bc')))"
['libreadline.so.7', 'libc.so.6']
```
2. Some old OpenCV build I found on my hard drive (https://files.pythonhosted.org/packages/67/50/665a503167396ad347957bea0bd8d5c08c865030b2d1565ff06eba613780/opencv_python-4.5.5.64-cp36-abi3-manylinux_2_17_x86_64.manylinux2014_x86_64.whl, running `unzip` beforehand):

```
$ ldd /path/to/cv2/cv2.abi3.so
linux-vdso.so.1 (0x00007fffc3f9c000)
libavcodec-65fa80df.so.58.134.100 => /path/to/cv2/../opencv_python.libs/libavcodec-65fa80df.so.58.134.100 (0x00007f8bcf2a3000)
libavformat-8ef5c7db.so.58.76.100 => /path/to/cv2/../opencv_python.libs/libavformat-8ef5c7db.so.58.76.100 (0x00007f8bcf024000)
libavutil-9c768859.so.56.70.100 => /path/to/cv2/../opencv_python.libs/libavutil-9c768859.so.56.70.100 (0x00007f8bced77000)
libswscale-e6451464.so.5.9.100 => /path/to/cv2/../opencv_python.libs/libswscale-e6451464.so.5.9.100 (0x00007f8bcece4000)
libQt5Widgets-e69d94fb.so.5.15.0 => /path/to/cv2/../opencv_python.libs/libQt5Widgets-e69d94fb.so.5.15.0 (0x00007f8bce3bf000)
libQt5Gui-ba0a2070.so.5.15.0 => /path/to/cv2/../opencv_python.libs/libQt5Gui-ba0a2070.so.5.15.0 (0x00007f8bcdab7000)
libQt5Test-c38a5234.so.5.15.0 => /path/to/cv2/../opencv_python.libs/libQt5Test-c38a5234.so.5.15.0 (0x00007f8bcda4c000)
libQt5Core-39545cc7.so.5.15.0 => /path/to/cv2/../opencv_python.libs/libQt5Core-39545cc7.so.5.15.0 (0x00007f8bcd349000)
libz.so.1 => /lib64/libz.so.1 (0x00007f8bcd30a000)
libopenblas-r0-f650aae0.3.3.so => /path/to/cv2/../opencv_python.libs/libopenblas-r0-f650aae0.3.3.so (0x00007f8bcac00000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f8bcd2e4000)
librt.so.1 => /lib64/librt.so.1 (0x00007f8bcd2da000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f8bcd2d5000)
libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00007f8bca9bb000)
libm.so.6 => /lib64/libm.so.6 (0x00007f8bca86f000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f8bcd2af000)
libc.so.6 => /lib64/libc.so.6 (0x00007f8bca678000)
/lib64/ld-linux-x86-64.so.2 (0x00007f8bd4173000)
libswresample-99364a1c.so.3.9.100 => /path/to/cv2/../opencv_python.libs/libswresample-99364a1c.so.3.9.100 (0x00007f8bcd28e000)
libvpx-1016051d.so.7.0.0 => /path/to/cv2/../opencv_python.libs/libvpx-1016051d.so.7.0.0 (0x00007f8bca37b000)
libbz2-a273e504.so.1.0.6 => /path/to/cv2/../opencv_python.libs/libbz2-a273e504.so.1.0.6 (0x00007f8bca000000)
libssl-b92f8066.so.1.1 => /path/to/cv2/../opencv_python.libs/libssl-b92f8066.so.1.1 (0x00007f8bcd1ed000)
libcrypto-09fe7800.so.1.1 => /path/to/cv2/../opencv_python.libs/libcrypto-09fe7800.so.1.1 (0x00007f8bc9cfe000)
libGL.so.1 => /usr/lib64/libGL.so.1 (0x00007f8bc9a00000)
libpng15-ce838cd1.so.15.13.0 => /path/to/cv2/../opencv_python.libs/libpng15-ce838cd1.so.15.13.0 (0x00007f8bc9600000)
libgthread-2.0.so.0 => /usr/lib64/libgthread-2.0.so.0 (0x00007f8bcd1ea000)
libglib-2.0.so.0 => /usr/lib64/libglib-2.0.so.0 (0x00007f8bca246000)
libgfortran-91cc3cb1.so.3.0.0 => /path/to/cv2/../opencv_python.libs/libgfortran-91cc3cb1.so.3.0.0 (0x00007f8bc9200000)
libGLX.so.0 => /usr/lib64/libGLX.so.0 (0x00007f8bc8e00000)
libGLdispatch.so.0 => /usr/lib64/libGLdispatch.so.0 (0x00007f8bc8a00000)
libpcre.so.1 => /usr/lib64/libpcre.so.1 (0x00007f8bc8600000)
libquadmath-96973f99.so.0.0.0 => /path/to/cv2/../opencv_python.libs/libquadmath-96973f99.so.0.0.0 (0x00007f8bc8200000)
libX11.so.6 => /usr/lib64/libX11.so.6 (0x00007f8bc98bf000)
libxcb.so.1 => /usr/lib64/libxcb.so.1 (0x00007f8bc7e00000)
libXau.so.6 => /usr/lib64/libXau.so.6 (0x00007f8bc7a00000)
$ python -c "from elf_inspector import elf; print(list(elf.get_elf_dependencies(location='/path/to/cv2/cv2.abi3.so')))"
['libavcodec-65fa80df.so.58.134.100', 'libavformat-8ef5c7db.so.58.76.100', 'libavutil-9c768859.so.56.70.100', 'libswscale-e6451464.so.5.9.100', 'libQt5Widgets-e69d94fb.so.5.15.0', 'libQt5Gui-ba0a2070.so.5.15.0', 'libQt5Test-c38a5234.so.5.15.0', 'libQt5Core-39545cc7.so.5.15.0', 'libz.so.1', 'libopenblas-r0-f650aae0.3.3.so', 'libpthread.so.0', 'librt.so.1', 'libdl.so.2', 'libstdc++.so.6', 'libm.so.6', 'libgcc_s.so.1', 'libc.so.6', 'ld-linux-x86-64.so.2']
```

My observations:

* *elf-inspector* only supports returning absolute paths for DWARF files. For Manylinux wheels like OpenCV, it is not clear where each dependency is used from.
* *elf-inspector* lists the `ld-linux-x86-64.so.2` and `libc.so.6` dependencies for OpenCV, while it does not for *bc*, although `ldd` states that both are linking to them.
* *bc* links against `libtinfo.so.6` according to `ldd`, but *elf-inspector* does not list it.

Is there an easy way to resolve these discrepancies and get rid of the limits of the current approach? At the moment, it seems like `ldd` is more reliable for this use case, but maybe I am just missing something important here.