please add file name as metadata

[alexlib]

Thanks for the great package. It works great. However, sometimes I read sequence in a folder numbered not from 0, but some arbitrary number and in some arbitrary name form, e.g. _cam_N_M.png where both N and M are integers, typically N = 1..10 and M = some range of integers, but not starting from 0. There are two things that I'm not sure about:
a) how are the sequences are sorted, i.e. is it first by the value of N and then by M ?
b) it would be quite easy to figure out if the frames would carry a metadata with a filename.

Thanks in advance for this extension

[alexlib]

I found that I can use ImageSequence._filepaths to get the list of files. It's basically sufficient for my case.

[nkeim]

Thanks. I'm surprised that ImageSequence doesn't expose the filenames more publicly; PIMS already has the infrastructure to do that (via propagate_attrs) in a way that follows slicing of sequences. I'm going to reopen this because it seems like a pretty good feature request!