Unclear what IImageFLAG does

[dnjohnstone]

Limited documentation here: https://github.com/RudoRoemer/Felix/blob/master/README.txt suggests that IImageFLAG=0 ought to produce a "montage" output but it doesn't seem to any more, now I think it maybe does something to do with whether "differences" are saved? IImageFLAG=2 also doesn't seem to return amplitues and phases anymore as documentation suggests.

In general the README.txt seems to be outdated.