Strip usages of IY register

forth/boot.fs

@@ -320,7 +320,7 @@ PC ORG @ 0x34 + ! ( execute )
 
 PC ORG @ 0x0f + ! ( compiledWord )
 ( Execute a list of atoms, which always end with EXIT.
-  IY points to that list. What do we do:
+  DE points to that list. What do we do:
   1. Push current IP to RS
   2. Set new IP to the second atom of the list
   3. Execute the first atom of the list. )

forth/z80c.fs

@@ -85,13 +85,13 @@ CODE 2OVER
     HL POPqq,       ( D )
     DE POPqq,       ( C )
     BC POPqq,       ( B )
-    IY POPqq,       ( A )
+    EXX, HL POPqq, EXX, ( A )
     chkPS,
-    IY PUSHqq,      ( A )
+    EXX, HL PUSHqq, EXX, ( A )
     BC PUSHqq,      ( B )
     DE PUSHqq,      ( C )
     HL PUSHqq,      ( D )
-    IY PUSHqq,      ( A )
+    EXX, HL PUSHqq, EXX, ( A )
     BC PUSHqq,      ( B )
 ;CODE
 
@@ -101,11 +101,11 @@ CODE 2SWAP
     HL POPqq,       ( D )
     DE POPqq,       ( C )
     BC POPqq,       ( B )
-    IY POPqq,       ( A )
+    EXX, HL POPqq, EXX, ( A )
     chkPS,
     DE PUSHqq,      ( C )
     HL PUSHqq,      ( D )
-    IY PUSHqq,      ( A )
+    EXX, HL PUSHqq, EXX, ( A )
     BC PUSHqq,      ( B )
 ;CODE