Consider adding information about the `Enum` class to the chapter on enumerations

[rbwhitaker]

I'm planning on doing a similar thing with Array and the arrays chapter. The catch with this one is that it makes far heavier use of typeof, Type, and generics, which makes it harder to embrace this early in the book.

[rbwhitaker]

A discussion, similar to what is covered in a blog post (http://csharpplayersguide.com/blog/2022/05/22/parsing-enumerations/), is now included in the enumerations chapter. It still needs some revising, but that is true of the whole book, so I'm calling this one done.