Convert sagews into sws

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A colleague asked if it is possible to convert from sagews into sws, so that he can use the notebooks that his students create on Sage Cloud.

I have found a sage-cloud thread which mentions this quick script.

My motivations for writing this questions are:

1. I thought ask.sagemath.org should have an answer to that question
2. There will be better ways in the future
3. There may be better ways now!

So feel free to contribute and keep this question up to date!

PD: For the record, sws files are compressed tar files that you can decompress with tar jxf %F. They contain an html file with code and comments, a pickle file with some python objects, a data folder with the attachments, and a cells folder with the images contained in the output of the cells. On the other hand, sagews files are plain text files with no attachments.