Add pixel loss functions, move warp

unsupervised/warp.py

@@ -0,0 +1,15 @@
+def projective_inverse_warp(target_img, source_img, depth, pose, intrinsics):
+    """
+    Calculate the reprojected image from the source to the target, based on the given depth, pose and intrinsics
+
+    SFM Learner inverse warp step
+        ps ~ K.T(t->s).Dt(pt).K^-1.pt
+
+    :param target_img: Tensor (batch, height, width, 3)
+    :param source_img: Tensor, same shape as target_img
+    :param depth: Tensor, (batch, height, width, 1)
+    :param pose: (batch, 3, 3)
+    :param intrinsics: (batch, 3, 3)
+    :return: The source image reprojected to the target
+    """
+    pass