Add suport for Response schemas (#10)

Schemas generated from Serializers will now be added to the `definitions` section by default, and used as `$ref` objects where needed.  
The Schema definition name is based on the serializer class name, and can be overriden by specifying a `__ref_name__` property on the Serializer. If this property is set to None, the schema will not be added to `definitions` and will be forced inline.

Closes #6, #7.

.coveragerc

@@ -14,6 +14,7 @@ exclude_lines =
 
     # Don't complain if tests don't hit defensive assertion code:
     raise AssertionError
+    raise TypeError
     raise NotImplementedError
     warnings.warn
 
@@ -21,6 +22,9 @@ exclude_lines =
     if 0:
     if __name__ == .__main__.:
 
+    # Don't complain if we don't hit invalid schema configurations
+    raise SwaggerGenerationError
+
 ignore_errors = True
 precision = 0