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

@@ -63,7 +63,7 @@ class DataSaver:
             saver.save("image.tif",image)
         """
 
-        folder = os.path.dirname(path)
+        folder = os.path.dirname(path) or '.'
         # Check if directory exists
         if os.path.isdir(folder):
             _, ext = os.path.splitext(path)