Add Go Doc comments for structs and their fields

[magnusbaeck]

Description

Now that we have the event documentation in structured form rather than just a bunch of Markdown files we should include this documentation in the generated code.

Motivation

If the package documentation includes event documentation you can almost use it as the sole documentation source when writing code that interprets or creates Eiffel events.

Exemplification

N/A

Benefits

• IDEs will be able to show documentation as you're writing your code.
• https://pkg.go.dev/github.com/eiffel-community/eiffelevents-sdk-go will describe the events.

Possible Drawbacks

None, except obviously more complexity in the code generation.