pcat: it works!

Forth intepreter now works! There's still DOES> and overflow checks
to implement, but otherwise, we have it!

blk/818

@@ -2,4 +2,4 @@
         DI 3 SUBxi, AX [DI] MOVx[], ( prev )
         AX AX ORxx,
     JNZ, AGAIN, ( loop )
-    AX INCx, ( NZ ) RETn,
+    SI DECx, ( start of string, and NZ ) RETn,

recipes/pcat/xcomp.fs

@@ -9,7 +9,8 @@ RS_ADDR 0x80 - CONSTANT RAMSTART
 CODE (emit)
     AX POPx, AH 0x0e MOVri, ( print char ) 0x10 INT,
 ;CODE
-CODE (key) AH AH XORrr, 0x16 INT, AX PUSHx, ;CODE
+CODE (key)
+    AH AH XORrr, 0x16 INT, AH AH XORrr, AX PUSHx, ;CODE
 380 LOAD  ( xcomp core high )
 (entry) _
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