Fix Flips documentation and tests errors caused by master merge

This adds missing documentation for the Flip transformations, and adds
FlipDim to the reference page. Also, fixes the "Big Pipeline/3D" unit
test that was failing due to not being able to compose two
ComposedProjectiveTransforms.

Author: paulnovo

docs/src/ref.md

@@ -6,6 +6,7 @@ BoundingBox
 CenterCrop
 CenterResizeCrop
 Crop
+FlipDim
 FlipX
 FlipY
 FlipZ

docs/src/transformations.md

@@ -26,6 +26,7 @@ Projective transformations include:
 Affine transformations are a subgroup of projective transformations that can be composed very efficiently: composing two affine transformations results in another affine transformation. Affine transformations can represent translation, scaling, reflection and rotation. Available `Transform`s are:
 
 ```@docs; canonical=false
+FlipDim
 FlipX
 FlipY
 FlipZ

src/DataAugmentation.jl

@@ -84,6 +84,7 @@ export Item,
     apply,
     Reflect,
     WarpAffine,
+    FlipDim,
     FlipX,
     FlipY,
     FlipZ,

src/projective/affine.jl

@@ -258,8 +258,11 @@ end
 
 """
     FlipDim{N}(dim)
+
 Reflect `N` dimensional data along the axis of dimension `dim`. Must satisfy 1 <= `dim` <= `N`.
+
 ## Examples
+
 ```julia
 tfm = FlipDim{2}(1)
 ```
@@ -269,15 +272,33 @@ struct FlipDim{N} <: ProjectiveTransform
     FlipDim{N}(dim) where N = 1 <= dim <= N ? new{N}(dim) : error("invalid dimension")
 end
 
-# 2D images use (r, c) = (y, x) convention
+"""
+    FlipX{N}()
+
+Flip `N` dimensional data along the x-axis. 2D images use (r, c) = (y, x)
+convention such that x-axis flips occur along the second dimension. For N >= 3,
+x-axis flips occur along the first dimension.
+"""
 struct FlipX{N}
     FlipX{N}() where N = FlipDim{N}(N==2 ? 2 : 1)
 end
 
+"""
+    FlipY{N}()
+
+Flip `N` dimensional data along the y-axis. 2D images use (r, c) = (y, x)
+convention such that y-axis flips occur along the first dimension. For N >= 3,
+y-axis flips occur along the second dimension.
+"""
 struct FlipY{N}
     FlipY{N}() where N = FlipDim{N}(N==2 ? 1 : 2)
 end
 
+"""
+    FlipZ{N}()
+
+Flip `N` dimensional data along the z-axis.
+"""
 struct FlipZ{N}
     FlipZ{N}() where N = FlipDim{N}(3)
 end

src/projective/compose.jl

@@ -26,6 +26,9 @@ compose(composed::ComposedProjectiveTransform, tfm::ProjectiveTransform) =
 compose(tfm::ProjectiveTransform, composed::ComposedProjectiveTransform) =
     ComposedProjectiveTransform(tfm, composed.tfms...)
 
+compose(composed1::ComposedProjectiveTransform, composed2::ComposedProjectiveTransform) =
+    ComposedProjectiveTransform(composed1.tfms..., composed2.tfms...)
+
 
 # The random state is collected from the transformations that make up the
 # `ComposedProjectiveTransform`: