Add export.c with support for exporting card states as key=value pairs.
Exports ALSA_CARD_NUMBER/ALSA_CARD_STATE for single cards, or
ALSA_CARD#_STATE for multiple cards. States: active, skip, waiting.
Add -Y (--export) option to restore command for state export.
This feature is designed for udev IMPORT{program} use.
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
