api: revise annotation naming and project structure

[elucash]

For one of the future versions, probably, before 1.0 (or for 1.0), there's intention to revise naming for the annotations, and package and module structure.
Driving factors for the changes:

• Need better modularization: annotations, packages, modules
• Simplicity and flexibility

While I liked initial straightforward @Generate* and .common - like approach for the toolkit, and other guys was ok with it, I no longer feel its a way to go.

Modules/packages:

• Split in large chunks: core immutables, JSON, repositories, etc.
• Annotation should go together with supporting classes for repositories and JSON.
• Decide if actual processor should go to separate modules (depends on testing with IDEs)

Annotation naming:

• Allow for both simple name and namespacing via annotation nesting. Currently don't know how it will work in practice, but currently I like this idea. Especially how it plays with different modules
• Examples: @Value.Immutable, @Value.Default, @Value.Parameter, @Value.Derived, @Json.Marshaler, @Json.Named, @Json.Ignore, @Mongo.Repository. This allows for autocompletion starting with enclosing annotation, and also allow import for simple annotation name, depending on style and mixing with other annotations.

As a "spoiler": all these exercises will be much more reasonable when new annotation processing and modeling toolkit will be ready (#17.)

[elucash]

• Annotation changes done
• Modules and packages are restructured, but not quite as it was planned. Anyway useful enough.