daala_ec: Convert the encoder to use iCDFs

This only changes the internal coding engine. We convert CDFs into
iCDFs at the "bool" writer <-> daala_ec boundary.

Encoder output should not change, and all streams should remain
decodable without decoder changes.

Change-Id: Id3ac7352926497bf6f7bc371ab9bc76e9a3569d5
4 files changed