Update message.py

Now, when doing
```py
for word in message:
    print(word)
```
it will print all the words of the message, which are separated by a space!

discord/message.py

@@ -451,6 +451,10 @@ class Message(Hashable):
         .. describe:: hash(x)
 
             Returns the message's hash.
+          
+        .. describe:: iter(x)
+            
+            Returns an iterator of words of the message, separated by a space
 
     Attributes
     -----------
@@ -606,6 +610,9 @@ class Message(Hashable):
 
     def __int__(self):
         return self.id
+    
+    def __iter__(self):
+        yield from self.content.split()
 
     def __repr__(self):
         return '<Message id={0.id} channel={0.channel!r} type={0.type!r} author={0.author!r} flags={0.flags!r}>'.format(self)