- Allow a duration of 0
- Rename LOOP chunk to ANIM and add the background color field to it.
- Add a disposal method field for each animation frame.
- Modify webpmux.c binary interface to allow the input of background color
and disposal methods. Also make '-loop' and '-bgcolor' arguments optional
with some default values.
Change-Id: I807372a61cdb8a0d3080ae3552caf2848070bf4d
fa30c86323