Add docstrings!

[josephsdavid]

With code cleaned up and (hopefully) working CI!

[codecov-commenter]

Codecov Report

Merging #209 (8aaa88f) into dev (b3fa3a8) will increase coverage by 0.75%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev     #209      +/-   ##
==========================================
+ Coverage   92.27%   93.03%   +0.75%     
==========================================
  Files           9        9              
  Lines         246      244       -2     
==========================================
  Hits          227      227              
+ Misses         19       17       -2     

Impacted Files	Coverage Δ
src/classifier.jl	100.00% <ø> (ø)
src/image.jl	100.00% <ø> (ø)
src/regressor.jl	100.00% <ø> (ø)
src/types.jl	100.00% <ø> (+14.28%)	⬆️

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[ablaom]

Great work. You have erred on the verbose side, which has made it easier to review 😉 . Please make the cuts suggested in annotations. Some of these could go into separate MLJFlux documentation (replacing current readme) but we'll need to come back to that later.

It's very nice to have the builder illustrations. One comment: I think we could use the macro for all of them, to save defining extra structs. In some models (classifiers?) you are still using the explicit definitions. And be sure to test all examples. They should be self-contained.

[ablaom]

Thanks @josephsdavid for your valuable contribution. 🎆