post-download implemented #4

[Spatenheinz]

I have considered your idea and it grew on me. So i have implemented post-download. I have not fixed anything in relation to the meta file etc. but i have moved unzipping submissions into a function unzip_handin() which works as a "macro". It is quite a bad implementation which should probably be improved some time in the future. Currently it should only work as a shortcut for generic unzipping.

[kfl]

I'll not merge this PR as it is currently.

• There is no documentation, thus I'm not sure I fully understand how to use the feature. I think that to get unzipping I need to set post-download to unzip_handin (or is it unzip_handin()).
• The feature is not "opt-in". That is, it changes the current behaviour of calling download.py without enabling the feature. This goes against one of my current core development principles for staffeli_nt: Adding features for one course, should not disturb other courses using staffeli_nt (especially not while we are mid-block).
• The current feature is just too dirty. Fishing variable binding out of the calling function's stack frame is too fragile for me to stomach 😉

That said, I like the idea of having some well-defined steps to use in post-download instead of having just raw python code. Perhaps something like:

post-download:
  - unzip_in("code.zip","unpacked")
  - remove_standard_junk
  - remove_junk([".stack-work",".git"])
  - call_onlineta:
      - url: https://pop.incorrectness.dk/
      - handin: code.zip

Maybe that's the right way forward for #4