GROOVY-6044: Add "incompatibleReturnType" handler for type checking extensions
Provides a more recent snapshot of the wiki
First stab at integrating the Asciidoc-based documentation and tests.

Documents should be placed in src/spec/doc of each modules, while tests to be included in those documents should live in src/spec/test.

Still needs to be done:
- collect all the generated documents and bundle them in the doc distro
- provide both the single page vs chuncked pages versions
- provide a PDF export (once Asciidoctor supports it itself)
GROOVY-5436: Enable use of parameter list in SQL IN Clause