parser: added doxygen tag for struct mpd_parser
parser: added doxygen tag for struct mpd_parser

cmende/libmpdclient,cmende/libmpdclient,yusiwen/libmpdclient,jagleeso/libmpdclient,sl0th/libmpdclient,jwise/libmpdclient,sl0th/libmpdclient,yusiwen/libmpdclient,yusiwen/libmpdclient,sl0th/libmpdclient,jwise/libmpdclient,jagleeso/libmpdclient,jwise/libmpdclient,jagleeso/libmpdclient,cmende/libmpdclient,psych0tik/libmpdclient2,psych0tik/libmpdclient2