Make square centre-padding a model transform

This MR fixes issues #23 (closed) and #39 (closed), by:

• Removing centre-cropping from all databases raw-data loaders
• Creating a SquareCenterPad transform that operates on tensors
• Adding that transform to all relevant models (Pasa, Alexnet, Densenet)

src/mednet/models/transforms.py

@@ -10,7 +10,7 @@ import torchvision.transforms.functional
 
 
 def square_center_pad(img: torch.Tensor) -> torch.Tensor:
-    """Returns a squared version of the image, centered on a canvas padded with
+    """Return a squared version of the image, centered on a canvas padded with
     zeros.
 
     Parameters
@@ -23,8 +23,7 @@ def square_center_pad(img: torch.Tensor) -> torch.Tensor:
     Returns
     -------
 
-    img
-        transformed tensor, guaranteed to be square (ie. equal height and
+        Transformed tensor, guaranteed to be square (ie. equal height and
         width).
     """
 
@@ -129,8 +128,7 @@ def rgb_to_grayscale(img: torch.Tensor) -> torch.Tensor:
 
 
 class SquareCenterPad(torch.nn.Module):
-    """Transforms to a squared version of the image, centered on a canvas
-    padded with zeros."""
+    """Transform to a squared version of the image, centered on a canvas padded with zeros."""
 
     def __init__(self):
         super().__init__()