Replace many lingering calls to exit() from the code,
replacing most with exception throws, which can be
caught by the existing mechanisms.
Update the option-parsing code to return an explicit
value indicating what to do (e.g., exit status to return
to the shell).
An upcoming commit will make the sound headers standalone, and no longer include various other headers / using std:: declarations. Prepare for this by making includes and usage of namespaces explicit.
