Add the rummy family: meld engine + Gin, Rummy, Rummy 500, Hand & Foot

Introduce a shared meld engine and four games built on it, all on
cg-core/EIEIO with console UNICODE rendering.

* cg-rummy.el: the meld engine and Gin Rummy.  Set/run validation,
  candidate-meld enumeration, a bitmask-DP minimum-deadwood partition,
  and a layoff finder, plus the abstract cg-rummy-game base and shared
  render helpers.  Gin is two-handed with draw/take/discard/knock, gin
  and undercut bonuses, opponent layoffs, and play to 100.

* cg-rum500.el: the abstract cg-tablemeld-game (one mode and command
  set, dispatching on the subclass) driving Basic Rummy (meld out;
  score the cards left in other hands; to 100) and Rummy 500 (score the
  cards you lay down, lose those left in hand; ace high and worth 15;
  to 500).

* cg-handfoot.el: Hand & Foot, a partnership Canasta cousin.  Hand and
  foot packets, Twos and Jokers wild, rank books with clean/dirty piles,
  go-out bonus, and partnership scoring to 5000.  Deliberately

README.org

@@ -60,6 +60,20 @@ with its command.
   beat it or pass; first out rules, last out scrubs, and the roles trade
   cards on the next deal.
 
+** Rummy
+- ~cg-gin~ -- Gin Rummy.  A two-handed duel: draw or take the discard,
+  build sets and runs, and knock once your deadwood is ten or less, or go
+  gin with none; your opponent then lays off and may undercut you.  First
+  to 100 wins.
+- ~cg-rummy-basic~ -- Rummy.  Meld sets and runs onto the table and lay
+  cards off onto them; empty your hand to go out and score the cards left
+  in the other hands.
+- ~cg-rum500~ -- Rummy 500.  As above, but you score the cards you lay
+  down and lose the cards left in your hand; first past 500 wins.
+- ~cg-handfoot~ -- Hand & Foot.  A partnership Canasta cousin: play a hand
+  and then a foot, build books of a rank with Twos and Jokers wild, and go
+  out once your side has completed two of them.
+
 * TODO
 - [X] make the suit symbols customizable (~cg-symbols~) and obey them
 - [ ] a Texinfo manual