moved loss and updated docstrings

src/model_modules/loss.py

+"""Collection of different customised loss functions."""
+
+from keras import backend as K
+
+from typing import Callable
+
+
+def l_p_loss(power: int) -> Callable:
+    """
+    Calculate the L<p> loss for given power p.
+
+    L1 (p=1) is equal to mean absolute error (MAE), L2 (p=2) is to mean squared error (MSE), ...
+
+    :param power: set the power of the error calculus
+
+    :return: loss for given power
+    """
+
+    def loss(y_true, y_pred):
+        return K.mean(K.pow(K.abs(y_pred - y_true), power), axis=-1)
+
+    return loss