GROOVY-5998: Using subscript operator on properties with a Builder and @DelegatesTo doesn't work

added non regression test
Make it clear that the template engine can be used to render any text based content
GROOVY-6788: Support for layouts/fragments in MarkupTemplateEngine
GROOVY-6788: Add missing test resource
GROOVY-6788: Add missing test resource (#2)
Add new template generators for Reader versions which take an optional template name, useful for error reporting