This is achieved by running the encoding process in a loop and
padding when we don't reach the exact rate. It also implements
VBR-with-cap, which means we no longer need to artificially decrease
the SILK bandwidth when it's close to the cap.
- increases the max pitch lag by 1 (the thing Tim pointed out). this brings the decoder in sync with the old one
- avoids that the first stereo frame is collapsed to mono
Simplifies mono/stereo switching in SILK
Fixes a quantization mismatch between encoder and decoder
Constrains the pitch lags in the same way in the encoder and decoder
