Add Daala's Entropy Coder to Thor#8

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tterribe wants to merge 4 commits intocisco:masterfrom

tterribe:entropy1

Commits on Nov 1, 2015

Add simple framing.
Timothy B. Terriberry
committed
Exit from fatal errors with abort()
Timothy B. Terriberry
committed
Omit split flags from rectangular blocks in keyframes.
Timothy B. Terriberry
committed
Add Daala's entropy coder to Thor.
Timothy B. Terriberry
committed