port DataLoader from Flux

[CarloLucibello]

Fix #13

[darsnack]

Doesn't this just overlap with DataLoaders.jl? That's already LearnBase.jl compatible and more full-featured. Seems like we'd rather port that over.

[codecov-commenter]

Codecov Report

Merging #22 (a185548) into main (dfc430d) will increase coverage by 0.24%.
The diff coverage is 92.30%.

@@            Coverage Diff             @@
##             main      #22      +/-   ##
==========================================
+ Coverage   88.73%   88.97%   +0.24%     
==========================================
  Files          13       14       +1     
  Lines         355      381      +26     
==========================================
+ Hits          315      339      +24     
- Misses         40       42       +2     

Impacted Files	Coverage Δ
src/dataloader.jl	92.30% <92.30%> (ø)

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[CarloLucibello]

I'm not familiar with DataLoaders.jl yet, so I'm porting Flux's one and the corresponding tests first so that we pinpoint a non-breaking replacement for Flux. I will port DataLoaders.jl in a second PR.

[CarloLucibello]

We want to port DataLoaders.jl here and not just reexport, right?

[darsnack]

We want to port DataLoaders.jl here and not just reexport, right?

Yeah that's right. And your plan sounds good just want to check in that the long term DataLoader will end up matching DataLoaders.jl. Having a non-breaking version first is a good idea.