Programs can now pin specific routines to specific vectors in SplitBit assembly. Added snake game.

Programs/testPrograms/diagnostics/pinnedVectorTaken.asm

@@ -0,0 +1,28 @@
+; Two vectors pinned to the same number.
+;
+; This is the mistake pinning makes possible: numbers the assembler hands out cannot
+; collide, and numbers a person writes down can. Since the whole point of a pinned number
+; is that something outside this program is going to use it, two names sharing one is a
+; disagreement that has to be caught here rather than discovered by whatever calls the
+; wrong one.
+;
+; The service names in services.asm sit at 16, 17 and 18, so a program that includes them
+; and pins its own trap at one of those is caught by this same check.
+
+#Program
+
+start:
+  SWI first
+  HALT
+
+firstHandler:
+  RETI
+
+secondHandler:
+  RETI
+
+#Vectors
+
+  Boot           start
+  first   0d20   firstHandler
+  second  0d20   secondHandler