Add example of a project with an external c library and python bindings

[Erotemic]

This is a somewhat MWE of a type of library that I'd like to wrap, but the other examples don't cover.

The basic idea is that there is:

• A standalone C library that can be built as a shared object
• A python wrapper library that has a cython code that links to the C library.

As setup this currently is not working. Running:

    # Build, view, install, and test the wheel
    python setup.py bdist_wheel
    unzip -l dist/my_python_package-1.0.0-*.whl

demonstrates the contents of the wheel as is:

Archive:  dist/my_python_package-1.0.0-cp38-cp38-linux_x86_64.whl
  Length      Date    Time    Name
---------  ---------- -----   ----
       74  2021-09-23 20:03   my_python_package/__init__.py
   207080  2021-09-23 20:03   my_python_package/_cython_wrapper.cpython-38-x86_64-linux-gnu.so
    15136  2021-09-23 20:03   my_python_package-1.0.0.data/data/src/cxx/libmy_c_module.so
      181  2021-09-23 20:03   my_python_package-1.0.0.dist-info/METADATA
       97  2021-09-23 20:03   my_python_package-1.0.0.dist-info/WHEEL
       18  2021-09-23 20:03   my_python_package-1.0.0.dist-info/top_level.txt
      661  2021-09-23 20:03   my_python_package-1.0.0.dist-info/RECORD
---------                     -------
   223246                     7 files

And when I install the wheel I get:

(pyenv3.8.6) joncrall@toothbrush:~/code/scikit-build-sample-projects/projects/clib-wrapper$     python -c "import my_python_package"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/joncrall/.pyenv/versions/3.8.6/envs/pyenv3.8.6/lib/python3.8/site-packages/my_python_package/__init__.py", line 1, in <module>
    from ._cython_wrapper import my_cython_func
ImportError: libmy_c_module.so: cannot open shared object file: No such file or directory

I can build this and make it work if I make libmy_c_module a static library instead of a shared one, but I'd like to fixup this example such that it works and demos how to use skbuild for this use case.