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)
Do not run the asciidoc documentation generation on JDK 5 as Gradle fails to generate a proxy for the AsciidoctorTask.
Better check for JDK 5
Move the check for existence of the asciidoc doc folder in the block checking JDK version
GROOVY-6216: Upgrade to ASM 4.1
    * move version numbers to variables
    * upgrade ASM to 4.1
    * upgrade Lucene example to Lucene 4.3.1
    * make "examples" task pass compilation
    * make "examples" task triggered by the "check" task
Fix typo (warning -> warn)
GROOVY-6215: Incorrect type inference with flow typing and switch statements
GROOVY-6219: Inferred return type of closures used as method call parameters is not used in method selection
GROOVY-5898: Sql.java throws IllegalStateException when comments contain quotes
fix handling of unterminated quote at end of string
Merge pull request #212 from jwagenleitner/GROOVY-5898

GROOVY-5898: Sql.java throws IllegalStateException when comments contain quotes
improve test robustness
improve build robustness
Merge branch 'master' into rlw-jdk8