Improvements to writing Aleph results to a given stream (write rules, features).

* [ALEPH6,NEW] Added write_features/0 and write_rules/0 to the public predicates. Thse require a setting though.
* [ALEPH6,FIX] aleph_portray/1 does not exist since it was intended to be a user-created extension (see the Aleph4+ manual, settings =portray-X=.
* [ALEPH6,FIX] Resetting directly after ILP removes the internal variables that are used by write_features/0 and write_rules/0. This is now relocated to the ILP prologue section.
* [ALEPH6,SC] Added a stream argument to all aleph_writeq/3 calls.
* [ALEPH6,SC] Added a stream argument to all aleph_portray/3 calls.
* [ALEPH6,SC] Added a stream argument to all show/2 calls.