Dyn methods: Use setattr

Not seeing any customizations that necessitate the use of the magic
method `__setattr__()` here, so using `setattr()` should be equivalent.
[[1]] [[2]]

Timeit is reporting 20 to 80us reductions in object instantation times,
all 20% drops relative to pydot 1.4.1.

No other changes in external behavior are expected.

[1]: https://stackoverflow.com/questions/14756289/setattrobject-name-value-vs-object-setattr-name-value
[2]: https://stackoverflow.com/questions/7559170/whats-the-difference-between-setattr-and-object-setattr

(This commit is part of a series of changes in how the `get_*`,
`set_*`, `create_*` and `write_*` methods are dynamically created.)

pydot.py

@@ -533,14 +533,14 @@ def create_attribute_methods(self, obj_attributes):
 
             # Generate all the Setter methods.
             #
-            self.__setattr__(
+            setattr(self,
                 'set_'+attr,
                 lambda x, a=attr :
                     self.obj_dict['attributes'].__setitem__(a, x) )
 
             # Generate all the Getter methods.
             #
-            self.__setattr__(
+            setattr(self,
                 'get_'+attr, lambda a=attr : self.__get_attribute__(a))
 
 
@@ -1723,7 +1723,7 @@ def new_method(
                 return self.create(
                     format=f, prog=prog, encoding=encoding)
             name = 'create_{fmt}'.format(fmt=frmt)
-            self.__setattr__(name, new_method)
+            setattr(self, name, new_method)
 
         for frmt in self.formats+['raw']:
             def new_method(
@@ -1734,7 +1734,7 @@ def new_method(
                     path, format=f, prog=prog,
                     encoding=encoding)
             name = 'write_{fmt}'.format(fmt=frmt)
-            self.__setattr__(name, new_method)
+            setattr(self, name, new_method)
 
     def __getstate__(self):