Doc update
Add support for jpeg images with non-multiple of 16 sizes.
Fixing typo in arugment 2 of the usage.
Makes pvq_encode() not overwrite the input data so we can rollback later
Splits scalar quantization into a separate function

Conflicts:
	src/decode.c
	src/encode.c
Adds block-level skip flag to save bits/symbols on inter frames
Encodes small small (within +/- 2) motion vectors using a single symbol

Also saves 7% on akiyo at -v 50
Joint skip symbol for both AC and DC

Conflicts:
	src/encode.c
	src/pvq_encoder.c
Using rollback for skip so we can use the exact rate

Improves performance at "medium rates". bd_rate on akiyo-qcif gives:

           RATE (%) DSNR (dB)
    PSNR -2.61122 0.176862
 PSNRHVS -3.19544 0.269844
    SSIM -2.22924 0.126447
FASTSSIM -3.14752 0.216077

Conflicts:
	src/pvq.c
	src/pvq_encoder.c
Cleanup: moves some od_adapt_ctx initialization to od_adapt_ctx_reset()
Doc: intra prob equation was flipped
Updates doxygen comments wrt issue 288