First version of save function + unit tests

Finished first version of qim3d.io.save() + unit tests. I am not sure what self.verbose is intended to do, so for the moment, I have just left it unused in init()

qim3d/io/save.py

@@ -94,7 +94,7 @@ def save(path,
         data (numpy.ndarray): The data to be saved  
         replace (bool, optional): Specifies if an existing file with identical path should be replaced. 
             Default is False.
-        compression (bool, optional): Specifies if the file should be saved with Deflate compression.
+        compression (bool, optional): Specifies if the file should be saved with Deflate compression (lossless).
             Default is False.
         **kwargs: Additional keyword arguments to be passed to the DataSaver constructor