Would be nice to have original file offset in OB/OW value and fragments

[jpambrun]

First off, thanks for writing such a nice library. I have been playing around with it for a few weeks and find it really easy to work with.

I realize this is not really the goad of this library, but it would be nice to be able to access the original file byte offsets on OB and OW vr types such as pixel data and LUTs. My use case is around indexing files, I don't need the pixel data as it streams, but would like to access only the appropriate byte range later. In fact, it would be even better if we could optionally disable buffering of the whole buffer to save memory while streaming.

I tried to figure out how to hook it up, but the flow is somewhat complex.. just something to think of..