Rewrite torchvision packaging

[ezyang]

Following a similar line of inquiry to pytorch/audio#217

@peterjc123 I haven't ported the Windows bits to the new infrastructure yet. If I have time later I'll look into it; I'm interested in whether or not we can reasonable do the Windows on CircleCI (so there's only one pipeline we have to look at.)

[codecov-io]

Codecov Report

Merging #1209 into master will decrease coverage by 0.39%.
The diff coverage is 33.33%.

@@            Coverage Diff            @@
##           master    #1209     +/-   ##
=========================================
- Coverage   65.58%   65.19%   -0.4%     
=========================================
  Files          74       74             
  Lines        5780     5784      +4     
  Branches      883      786     -97     
=========================================
- Hits         3791     3771     -20     
- Misses       1724     1739     +15     
- Partials      265      274      +9

Impacted Files	Coverage Δ
torchvision/datasets/utils.py	59.35% <0%> (-1.3%)	⬇️
torchvision/io/video.py	71.31% <37.5%> (-0.69%)	⬇️
torchvision/datasets/cifar.py	71.26% <0%> (-6.9%)	⬇️
torchvision/datasets/folder.py	79.48% <0%> (-2.57%)	⬇️
torchvision/datasets/voc.py	20.87% <0%> (-2.2%)	⬇️
torchvision/datasets/lsun.py	20.83% <0%> (-2.09%)	⬇️
torchvision/transforms/transforms.py	79.76% <0%> (-1.18%)	⬇️
torchvision/transforms/functional.py	70.52% <0%> (-0.58%)	⬇️

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[peterjc123]

@ezyang That's not possible since CircleCI doesn't support Windows.
Update: Looks like there is early access for Windows: https://discuss.circleci.com/t/windows-early-access-now-available-on-circleci/30977

[ezyang]

@peterjc123 Yep. I should be able to get us expedited though.

[ezyang]

@peterjc123 OK, Windows CPU is enabled. Docs are at https://circleci.com/docs/2.0/hello-world-windows/

[fmassa]

I'm approving this, but I have a few questions regarding a few changes.

Also, I didn't check the new circle ci config very closely.

[ezyang]

@peterjc123 I'm leaving some of the old files around so maybe the Windows pipeline keeps working; I don't know how to test it, if you let me know I can try and fix it as well for the file changes