Merge #1729

1729: Adds affine and track_stats params to BatchNorm docstring r=DhairyaLGandhi a=Mottl

### PR Checklist

- [ ] Tests are added
- [ ] Entry in NEWS.md
- [*] Documentation, if applicable
- [ ] API changes require approval from a committer (different from the author, if applicable)


Co-authored-by: Dmitry Mottl <dmitry.mottl@gmail.com>

Author: bors[bot]

src/layers/normalise.jl

@@ -199,6 +199,7 @@ end
 """
     BatchNorm(channels::Integer, λ=identity;
               initβ=zeros32, initγ=ones32,
+              affine = true, track_stats = true,
               ϵ=1f-5, momentum= 0.1f0)
 
 [Batch Normalization](https://arxiv.org/abs/1502.03167) layer.