Organize project into a reusable library

[ctubbsii]

• Use {@code} in javadocs for maintainability
• Replace some loops with functional code
• Inline some trivial methods
• Create flexible API for reporting type problems
• Create separate ClassUtils for getting class info
• Create separate PublicApi class for defining a public API to be analyzed
• Separate analyzer code into its own Apilyzer class that takes a provided PublicApi and analyzes it independently of any Maven functionality. Separating the reponsibilities of different code components makes the code a bit more organized, and testable.

[ctubbsii]

@keith-turner I had to update this project recently to fix the build with JDK 21 (see 925d716ec4d55724b05f7a3c712804105c2a794e), and I ran across this old branch that I had forgotten about. I rebased and tested it, and it seems like it's a reasonable improvement to the code organization. Maybe not fully ready as a reusable library, but probably good enough that it can merge with the main branch.