Add additional GroovyClassLoader tests

These tests specifically test for compliance with parts of JLS Section 5.
GROOVY-6840: Create new ArrayList instead of returning empty lists for JSON Parsing
GROOVY-6840: Fix Typo
GROOVY-6840: Add Test Case for Empty Lists
Documentation for spread dot and spread method argument operators
GROOVY-6617: joint compiler fails to compile groovy class implemented java interface
improve javadoc
GROOVY-6404: Incorrect stubs for enums without constants
GROOVY-6302: Stub generator chokes on multi-dimensional arrays
GROOVY-4248: JavaStubGenerator doesn't generate annotations available in Groovy code (support Parameter annotations)
GROOVY-6855: Groovy annotations that support closures don't get stubs generated correctly
GROOVY-6855: Groovy annotations that support closures don't get stubs generated correctly (fix too eager commit)
Documentation for more operators:
   * fix rendering glitches
   * spread list
   * spread map
   * range
   * spaceship
   * subscript
Documentation for missing operators:
   * membership operator
   * identity operator
   * coercion operator
   * diamond operator
   * "call" operator
Use the new stylesheet for the asciidoctor documentation
Added documentation for Statements
Merge pull request #448 from grantmcconnaughey/documentation

GROOVY-6268: Documentation on Statements
GROOVY-6868: Upgrade SLF4J to 1.7.6 and Logback to 1.1.2
Merge pull request #434 from kaendfinger/GROOVY-6840

GROOVY-6840: JSON: Use ArrayList for Empty Lists
More tweaks to the documentation CSS for a more elegant typography title size scale