Flat matrix option to make comparison with scalar easier

Conflicts:
	src/internal.h
Better tuning of K as a function of N

Refined the model to better match the experimental rate-distortion curve
Adapt expectation of theta as fraction of max_theta for keyframes

Saves ~0.3% on bitrate, or about 10% of the bits used for theta
Adds inter-band masking for the remaining bands using a matrix

           RATE (%) DSNR (dB)
    PSNR -0.202785 0.0146348
 PSNRHVS -0.113397 0.0106145
    SSIM 0.0323708 -0.00216776
FASTSSIM -0.218771 0.00805372
Reinitialize od_state probs on every frame

Conflicts:
	src/pvq_decoder.c
	src/pvq_encoder.c
configure: use AC_CONFIG_AUX_DIR

Copied/generated files will be stored in the build-aux directory
Speed up early adaptation of the generic model

Saves about 0.3% for the same output
Separate quantization matrices for Cb and Cr