A Builder for RuleSets. Create a RuleSet by calling the ruleset
method, passing in a Closure defining the contents of the RuleSet.
The Closure can contain any combination of the following (as well as
arbitrary Groovy code):
ruleset - to load a RuleSet file. The path specifies either a
Groovy file or an XML file.rule - to load a single Rule (specify either the rule name or rule class)description - description of the RuleSet (optional)