Fixed misinterpretation of dtex samples in deepopacity case, updated README, comments, and ChangeLog to reflect fix.
Merge branch 'develop' of https://github.com/openexr/openexr into develop
This commit fixes several problems with DtexToEXR.

1: The files were flipped upside down. This is fixed.

2: The files were transposed rather than rotated with the --sideways flag, which has now
been fixed as well.

3: The data window was the wrong size, this has been fixed.

4: The default options are now are true for deep rgb, and the command line usage has been changed to
reflect these new defaults.