Apply mypy fixes, add comment to the unclear part

Author: Felixoid

zenmoney/diff.py

@@ -51,6 +51,8 @@ def __init__(self,
                  **kwargs,
                  ):
         for class_name in API_OBJECTS + ['Deletion']:
+            # Objects in the API are in camelCase,
+            # but in python are in PascalCase
             attr_name = class_name[0].lower() + class_name[1:]
             attr_value = locals()[attr_name]
             if attr_value:

zenmoney/oauth2.py

@@ -32,7 +32,7 @@ def __get_token(self):
             self.__set_token()
             return self._token
 
-    def __set_token(self):
+    def __set_token(self, _: None = None) -> None:
         'request cookie'
         'request code'
         'request token'

zenmoney/request.py

@@ -29,7 +29,7 @@ def diff(self, diff: Diff, debug=False) -> Diff:
 
         return Diff(**response.json())
 
-    def suggest(self, transaction: object) -> Transaction:
+    def suggest(self, transaction: Transaction) -> Transaction:
         '''
         Accept one or ZenObjectsList of Transactions
         returns the same data with suggestions