Return False: Solid Collision Between Actors

* Implement the handler code for `return false` when actors are
  colliding with each other and wish to act like solid walls.
* The locked doors will `return false` when they're closed and the
  colliding actor does not have the matching key.
* Add arbitrary key/value storage to Actors. The colored keys will set
  an actor value "key:%TITLE%" on the one who touched the key before
  destroying itself. The colored doors check that key when touched to
  decide whether to open.
* The trapdoor now only opens if you're touching it from the top (your
  overlap box Y value is 0), but if you touch it from below and the door
  is closed, it acts like a solid object.

rect_test.go

@@ -54,6 +54,16 @@ func TestIntersection(t *testing.T) {
 			B:      newRect(0, -240, 874, 490),
 			Expect: false, // XXX: must be true
 		},
+		{
+			A:      newRect(0, 30, 9, 62),
+			B:      newRect(16, 0, 32, 64),
+			Expect: false,
+		},
+		{
+			A:      newRect(0, 30, 11, 62),
+			B:      newRect(7, 4, 17, 28),
+			Expect: false,
+		},
 	}
 
 	for _, test := range tests {