MINOR: stream: Replace last_rule_file/line fields by a more generic field
The last evaluated rule is now saved in a generic structure, named
last_entity, with a type to identify it. The idea is to be able to store
other kind of entity that may interrupt a specific processing.
The type of the last evaluated rule is set to 1. It will be replace later by
an enum to be more explicit. In addition, the pointer to the rule itself is
saved instead of its location.
The sample fetch "last_entity" was added to retrieve the information about
it. In this case, it is the rule localtion, the config file containing the
rule followed by the line where the rule is defined, separated by a
colon. This sample fetch is not documented yet.