[daala] New generation entropy coder

[Timothy B. Terriberry]

I got to here:

"The advantage of Huffman is that we can adaptively modify the tree on 
the run, but we could also do it in ANS - switch some appearances 
between symbols and renumerate the following ones ... but it would be 
costly for a large table."

...and stopped. That's probably going to be a deal-breaker. The whole 
point of arithmetic coding is the flexibility in the modeling (which 
puts adaptive Huffman to shame), and we rely on this extensively. For 
the record, the entropy coder in Daala does not require multiplications 
or divisions, nor large tables. I encourage you to check it out.