Define new Linear/Bezier animation_types using less bits

[felicialim]

From the discussion at #892,

The start_point_values of the other subblocks except the first subblock of a parameter substream can be replaced by the end_point_values of the previous subblocks.

[jwcullen]

The issue was raised regarding positions. Maybe it is obvious, but we should consider allowing this for mix gains (in new profiles).

I think most practical uses would avoid discontinuities in mix gain, and could use this new animation for bit-rate savings. They could start based on the end of the previous subblock. Perhaps even the final subblock in the previous Parameter Block.