Make some changes in introduction docs

docs/main/introduction/di_in_python.rst

@@ -1,6 +1,9 @@
 Dependency injection and inversion of control in Python
 -------------------------------------------------------
 
+History
+~~~~~~~
+
 Originally, dependency injection pattern got popular in languages with static 
 typing, like Java. Dependency injection framework can 
 significantly improve flexibility of the language with static typing. Also,
@@ -14,6 +17,9 @@ for Java. Also there is a meaning that dependency injection framework is
 something that Python developer would not ever need, cause dependency injection
 could be implemented easily using language fundamentals.
 
+Discussion
+~~~~~~~~~~
+
 It is true. 
 
 Partly.
@@ -75,6 +81,9 @@ Main design purposes of using inversion of control are:
   instead rely on contracts.
 + To prevent side effects when replacing a module.
 
+Example
+~~~~~~~
+
 Let's go through next example:
 
 .. literalinclude:: ../../../examples/ioc_demo/car_engine_1.py

docs/main/introduction/structure.rst

@@ -8,11 +8,15 @@ interaction between each other.
     :width: 100%
     :align: center
 
-There are 3 main entities:
+There are 3 main entities: providers, injections and catalogs.
 
-.. glossary::
++ All of the entities could be used in composition with each other or 
+  separatelly.
++ Each of the entities could be extended via specialization.
 
 Providers
+~~~~~~~~~
+
 Providers are strategies of accesing objects. For example, 
 :py:class:`dependency_injector.providers.Factory` creates new instance 
 of provided class every time it is called. 
@@ -23,6 +27,8 @@ There are 3 main entities:
 :py:class:`dependency_injector.providers.Provider`.
 
 Injections
+~~~~~~~~~~
+
 Injections are instructions for making dependency injections 
 (there are several ways how they could be done). Injections are used 
 mostly by :py:class:`dependency_injector.providers.Factory` and 
@@ -31,12 +37,8 @@ There are 3 main entities:
 :py:class:`dependency_injector.injections.Injection`.
 
 Catalogs 
+~~~~~~~~~
+
 Catalogs are collections of providers. They are used for grouping 
 of providers by some principles. Base class is - 
 :py:class:`dependency_injector.catalogs.DeclarativeCatalog`.
-
-Some general principles about *Dependency Injector* entities:
-
-+ All of the entities could be used in composition with each other or 
-  separatelly.
-+ Each of the entities could be extended via specialization.

examples/di_demo/di_example.py

@@ -8,9 +8,7 @@ class Components(catalogs.DeclarativeCatalog):
     """Components catalog."""
 
     service = providers.Factory(Service)
-
-    client = providers.Factory(Client,
-                               service=service)
+    client = providers.Factory(Client, service=service)
 
 
 if __name__ == '__main__':