Current commit is just an API template for the rest of the code, and
I will add inner logic later.
Altref frames generate a lot of bitrate and at the same time
other frames refer to them a lot, so it makes sense to apply
special compensation-based adaptive quantization scheme for altref
frames. E.g., for blocks that are good predictors for the future
apply rate-control chosen quantizer while for bad predictors apply
worse one.
Change-Id: Iba3f8ec349470673b7249f6a125f6859336a47c8
