refactor __init__ of file package

mu_map/file/__init__.py

 import os
 
-from mu_map.file.dicom import load_dcm
+from mu_map.file.dicom import load_dcm, load_dcm_img
 from mu_map.file.dicom_to_interfile import to_interfile
-from mu_map.file.interfile import load_interfile, Interfile
+from mu_map.file.interfile import load_interfile, load_interfile_img, Interfile
 
-def load_as_interfile(filename: str) -> Interfile:
+def is_dicom(filename: str):
     _, ext = os.path.splitext(filename)
-    if ext == ".dcm":
-        return to_interfile(*load_dcm(filename))
+    return ext == ".ext"
 
-    return load_interfile(filename)
+def load_as_interfile(filename: str) -> Interfile:
+    if is_dicom(filename):
+        return to_interfile(*load_dcm(filename))
+    else:
+        return load_interfile(filename)
 
         
+def load_img(filename: str) -> Interfile:
+    if is_dicom(filename):
+        return load_dcm_img(filename)
+    else:
+        return load_interfile_img(filename)