Improvements to the serialization tests

* Utilized the FluentAssertions library
* Added assertion to the CircularReference test (the console dump had to go :-( )
* Changed visibility of the help classes to public to suppress nagging warnings
* Added Trait attribute for bug fix tests instead of a comment
* Lines of yaml is formed from multiple strings rather than splitting
* Used the generic Deserialize method so that the result is casted.
Abstracted the StringReader creation.
Rearranged and renamed methods.

* The first half of methods are sorted by feature and within feature by the order [serialize, deserialize, roundtrip]
* The second half of methods tests more inconsequential features
* Added a test enum instead of one from System.Drawing
Merge pull request #60 from rogernorling/refactor-serialization-test

Refactor of the serialization tests