Add C++ examples

[darbyjohnston]

It would be nice to have C++ examples demonstrating use of the OTIO API similar to the Python examples. Ideally the example code would be as similar as possible between C++ and Python so that new developers could see how the API is used in each language.

This could also address these issues:
#796
#171

I've done some initial work on this and converted the example "summarize_timing.py" to C++; I'll open a PR for the changes, though it is still a WIP...

[darbyjohnston]

I've added these C++ examples that correspond to the Python examples:

• conform.cpp
• flatten_video_tracks.cpp
• summarize_timing.cpp

I did not add a corresponding C++ example for shot_detect.py, since that calls ffprobe as a sub-process which is a bit tedious to do in C++.

I also added examples for using the Python adapters from C++:

• python_adapters_child_process.cpp
• python_adapters_embed.cpp

#918
#995