Update documentation

documentation/Introduction/how_to_use_the_library.md

@@ -1,3 +1,5 @@
 # How to Use the Library
 
 The C Macro Collections Library comes with very powerful data structures and they are only one macro away from you.
+
+TODO

documentation/Introduction/why_this_library.md

@@ -15,4 +15,4 @@ All with the following features:
 * __Nesting__ - Collections can be nested (List of Lists, HashSet of Stacks, etc);
 * __One macro to rule them all__ - Only one macro to generate everything and that's it.
 
-and many other powerful features (see [Features](../Features/features.html)).
+and many other powerful features (see [Features](../Overview/features_overview.html)).