Implemented NSArray serialization

It serializes by serializing its own elements and wrapping them with braces.
Implemented NSNumber serialization

It serializes with default behaviour
Found and fixed format error
Implemented NSSet serializations.

Works the same as NSArray serialization.
Implemented NSDictionary serializations.

All the same, with very little changes.
NSNull serialization.

Just returning description, nothing special.
Structure change.
Serialization for CGRect
Added main.m in order to compile.

Before that project wasn't able to be compiled, but now it can.
.gitignore deleted
Added metadata for this project
Moved to protocol using.

It's better to have unified protocol in order to ensure that every serializable class has method with the same required signature. And it's useful: one error was fixed just after this improvement.
Error fix
Serializer class implemented.

But it only does serialization without checking if there is NSDictionary in the root. Yet.
Added checking class.

It checks if NSDictionary was passed as parameter, and, if positive, passes it to its own nit checking superclass.
Serialization of inner elements delegated to unchecked serializer objects

It's better, because of preventing unused error creating