Move UploadNotAllowed exception into separate module

Also, add it back to the public API.

It has to be importable, otherwise it is hard to catch it :-)

modified:   src/flask_uploads/__init__.py
new file:   src/flask_uploads/exceptions.py
modified:   src/flask_uploads/flask_uploads.py

src/flask_uploads/__init__.py

@@ -14,6 +14,8 @@
 from .flask_uploads import lowercase_ext
 from .flask_uploads import config_for_set
 
+from .exceptions import UploadNotAllowed
+
 from .flask_uploads import ALL
 from .flask_uploads import AllExcept
 from .flask_uploads import TEXT
@@ -52,4 +54,5 @@
     "SOURCE",
     "EXECUTABLES",
     "DEFAULTS",
+    "UploadNotAllowed",
 ]

src/flask_uploads/exceptions.py

@@ -0,0 +1,6 @@
+class UploadNotAllowed(Exception):
+    """This exception is raised if the upload was not allowed.
+
+    You should catch it in your view code and
+    display an appropriate message to the user.
+    """

src/flask_uploads/flask_uploads.py

@@ -21,6 +21,8 @@
 from werkzeug.datastructures import FileStorage
 from werkzeug.utils import secure_filename
 
+from .exceptions import UploadNotAllowed
+
 PY3 = sys.version_info[0] == 3
 
 if PY3:
@@ -91,13 +93,6 @@
 DEFAULTS = TEXT + DOCUMENTS + IMAGES + DATA
 
 
-class UploadNotAllowed(Exception):
-    """
-    This exception is raised if the upload was not allowed. You should catch
-    it in your view code and display an appropriate message to the user.
-    """
-
-
 def extension(filename):
     ext = os.path.splitext(filename)[1]
     if ext.startswith('.'):