* look at possible overflow/precision issues in integer port

* redo all bit allocation if previous frame had zero_snr_offsets
* make dynrng work in dual-channel streams

* implement A/52a downmix extensions
* reduce size of delay buffer by 50%
* include float->s16 conversion in liba52 API ?
* include up/downsampling 44100<->48000 in liba52 API ?
* include audio dithering in liba52 API ?
* API extensions might be at a different level (base vs. extended)

* use restrict pointers where appropriate
* avoid overflows, including reading the a52 stream !!!
* faster bitstream parsing ?
* make dither code faster (generate dither table in advance ?)
* SIMD optimizations