add a new DeclarativePolicy framework

lib/declarative_policy.rb

lib/declarative_policy/base.rb

lib/declarative_policy/cache.rb

lib/declarative_policy/condition.rb

lib/declarative_policy/dsl.rb

lib/declarative_policy/preferred_scope.rb

lib/declarative_policy/rule.rb

lib/declarative_policy/runner.rb

lib/declarative_policy/step.rb