adx: add an ADX parser.

This simplifies the decoder so it doesn't have to process an in-packet header
or handle arbitrary-sized packets. It also fixes decoding of files with large
headers.

libavcodec/allcodecs.c

@@ -388,6 +388,7 @@ void avcodec_register_all(void)
     REGISTER_PARSER  (AAC, aac);
     REGISTER_PARSER  (AAC_LATM, aac_latm);
     REGISTER_PARSER  (AC3, ac3);
+    REGISTER_PARSER  (ADX, adx);
     REGISTER_PARSER  (CAVSVIDEO, cavsvideo);
     REGISTER_PARSER  (DCA, dca);
     REGISTER_PARSER  (DIRAC, dirac);