Renamed Block Codec to BWT Block Codec. Other cosmetic changes.
Explicitely reserve extra header bits instead of letting them spill to block size.
Tweak implementation to improve compression ratio a little bit.
Simplify context resizer constructor.
Provide a scaling factor rather than a number of geodesics to better handle the
case where both directions are selected.
Improve slightly thep erformance of the DWT color sampler.