Add Windows support - Fix tests, enable CI, and release Windows binaries

[mterrel]

Fixes #778

With these changes, all tests pass running on a Windows system with Docker in Linux container mode.
One test file cannot run if Docker is in Windows container mode because crane can only pull Linux containers.

I'm not normally a Go developer, so let me know if I need to make any changes to how I've done anything here.

Please take a hard look at the "unclosed ReadClosers" fix, as that one is the most involved and has the most potential for me to have done something incorrectly.

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[mterrel]

@googlebot I signed it!

[codecov-io]

Codecov Report

Merging #780 into master will increase coverage by 0.05%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master     #780      +/-   ##
==========================================
+ Coverage   75.54%   75.60%   +0.05%     
==========================================
  Files         102      102              
  Lines        4171     4185      +14     
==========================================
+ Hits         3151     3164      +13     
  Misses        566      566              
- Partials      454      455       +1     

Impacted Files	Coverage Δ
pkg/v1/cache/fs.go	70.00% <88.88%> (+1.48%)	⬆️
pkg/v1/mutate/mutate.go	71.97% <100.00%> (+0.36%)	⬆️
pkg/v1/tarball/image.go	77.77% <100.00%> (+0.75%)	⬆️
pkg/v1/tarball/layer.go	73.33% <100.00%> (+0.45%)	⬆️

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[mterrel]

@jonjohnsonjr Are there any questions I can answer or anything you need from me on this PR?

[jonjohnsonjr]

any questions I can answer or anything you need from me on this PR?

Not yet! I'm currently in the process of moving, so my life is a bit hectic at the moment. Hopefully I'll be able to give this a proper review by the end of the week (no promises!).

Apologies for the delay, I really appreciate your contribution here.

[mterrel]

any questions I can answer or anything you need from me on this PR?

Not yet! I'm currently in the process of moving, so my life is a bit hectic at the moment. Hopefully I'll be able to give this a proper review by the end of the week (no promises!).

Apologies for the delay, I really appreciate your contribution here.

No worries. I know how all-consuming moving can be. Hope all goes well!

[jonjohnsonjr]

One test file cannot run if Docker is in Windows container mode because crane can only pull Linux containers.

Let's try that again when #742 lands.

[mterrel]

@jonjohnsonjr Ok, I made the requested changes and rebased to master.

[jonjohnsonjr]

Thanks so much for this!

[mterrel]

@jonjohnsonjr Would it be possible to publish a release that contains these changes?

[jonjohnsonjr]

Certainly! I'm juggling a few things but I want to test #851 against travis and get it merged before I cut a new release. Hopefully I can get to it by the end of today (and if you see anything glaringly wrong about that PR, please let me know).

[mterrel]

@jonjohnsonjr Awesome! Thanks for the new release! 😃