Add missing texinfo docstrings to all audio functions * libinterp/dldfcn/__player_audioplayer__.cc, libinterp/dldfcn/__recorder_audiorecorder__.cc, scripts/audio/@audioplayer/subsasgn.m, scripts/audio/@audioplayer/subsref.m, scripts/audio/@audiorecorder/__get_properties__.m, scripts/audio/@audiorecorder/subsasgn.m, scripts/audio/@audiorecorder/subsref.m: Add texinfo docstrings to all functions, internal or otherwise.