Updates to video_capture program

[adarshp]

This PR implements the following updates to the video_capture program.

• The --out_dir argument can now have tildes (thanks @manujinda !)
• The CMakeLists.txt files have been refactored for greater modularity (e.g., better to not depend on Portaudio to build the video capture program)
• The build invocation in README.md has been updated to include the correct flags for libfmt9.
• all the program options are now optional, in order for the --help option to actually work properly (it was throwing an exception earlier).

[adarshp]

@paulosoaresua - sure thing, we can hold off for now and you can merge it whenever you are ready.