Fix type of value parameter in setColor 

Parameter value receives Strings as options.getOptionValue returns string. This fixes --color option.
minor refactor: improved error message in utility method,
GROOVY-6708: Fix trait inheriting from other generic trait leading to compilation error
Introduced local variable of type boolean
Merge pull request #387 from vihangd/master

Fix type of value parameter in setColor
GROOVY-6698: fix "jarAll" task not taking the project jars into account, resulting in wrong "up-to-date" status
Documented stackable traits
Simplify semantics of traits by removing the @ForceOverride annotation and making override the default
Document inheritance of trait state gotchas
minor refactor: a few utility methods
@Builder spike for Groovy - initial commit
the actual AST transform
Fix typo in documentation of traits
Document multiple inheritance of traits
Fix typo in documentation of traits
Document multiple inheritance of traits
doco for ExternalStrategy
ignore Eclipse files of groovy-nio subproject
fixed path to sources of groovy-templates subproject
additional tests and doco