For a 0.16 release

[ablaom]

490, #492

For the release notes:

• (breaking) Modify the output of fitted_params for the following models, to bring them into line with other MLJ models: Standardizer, Discretizer, OneHotEncoder. See the updated doc-strings for the new format (#444, PR #490)

[codecov-commenter]

Codecov Report

Merging #491 (7214811) into master (1c813c2) will decrease coverage by 0.34%. The diff coverage is 25.00%.

@@            Coverage Diff             @@
##           master     #491      +/-   ##
==========================================
- Coverage   77.43%   77.08%   -0.35%     
==========================================
  Files          16       16              
  Lines        1121     1126       +5     
==========================================
  Hits          868      868              
- Misses        253      258       +5     

Impacted Files	Coverage Δ
src/builtins/Transformers.jl	95.38% <25.00%> (-1.02%)	:arrow_down:

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[ablaom]

Merging despite the check_registry fail, which has known unrelated cause and is tracked: https://github.com/JuliaAI/MLJModels.jl/issues/493 . I have tested the registry locally and it's fine.