Update introduction docs and examples

docs/main/introduction/di_in_python.rst

@@ -86,12 +86,12 @@ Example
 
 Let's go through next example:
 
-.. literalinclude:: ../../../examples/ioc_demo/car_engine_1.py
+.. literalinclude:: ../../../examples/ioc_di_demo/car_engine_1.py
    :language: python
 
 ``Car`` **creates** an ``Engine`` during its creation. Really? Does it make 
 more sense then creating an ``Engine`` separatelly and then 
 **put (inject) it into** ``Car`` when ``Car`` is being created?
 
-.. literalinclude:: ../../../examples/ioc_demo/car_engine_2.py
+.. literalinclude:: ../../../examples/ioc_di_demo/car_engine_2.py
    :language: python

examples/ioc_demo/car_engine_1.py

@@ -1,18 +0,0 @@
-"""Car & Engine example 1."""
-
-
-class Engine(object):
-    """Example engine."""
-
-
-class Car(object):
-    """Example car."""
-
-    def __init__(self):
-        """Initializer."""
-        self.engine = Engine()
-
-
-if __name__ == '__main__':
-    car = Car()
-    assert car.engine is not None

examples/ioc_demo/car_engine_2.py

@@ -1,18 +0,0 @@
-"""Car & Engine example 2."""
-
-
-class Engine(object):
-    """Example engine."""
-
-
-class Car(object):
-    """Example car."""
-
-    def __init__(self, engine):
-        """Initializer."""
-        self.engine = engine
-
-
-if __name__ == '__main__':
-    car = Car(Engine())
-    assert car.engine is not None

examples/ioc_di_demos/ioc_container_example.py

@@ -1,10 +1,8 @@
 """The Code, that uses IoC container."""
 
-from dependency_injector import catalogs
+from dependency_injector import catalogs, providers
-from dependency_injector import providers
 
-from ioc_example import Service
+from ioc_example import Service, Client
-from ioc_example import Client
 
 
 class Components(catalogs.DeclarativeCatalog):