Support including another rule set

[mohsen]

Could you please support an inclusion mechanism so that a rule set can be included into another one. In our case, we have a CMS with several custom URLs, each for a customer. We also have several general custom URLs which are shared for all customers. It's very good if we can have a base file, for general rules, and one rule set per client. Then we can include general rule set into customer-specific rule set,