add defines for sound functions
 SOUND_VOLUME, SOUND_BALANCE, SOUND_CHANNELS, SOUND_STEREO_WIDTH ...
 defines depend on target
 require "sound_defines" to add them to rb.sound_settings[]

consolidates:
 sound_set, sound_current, sound_default, sound_min, sound_max,
 sound_unit, sound_pitch, sound_val2phys to a single function

 rb.sound("name", setting, [value])

 require "sound.lua" for old functionality

Change-Id: Ice695218aa433f4fcbb48fbd6b8a9bf29c994110