Assemble psych and include it in the build. (#232)

Psych was added to the build system. It requires fops.s
for maths. Two notable things need to be fixed to make it
assemble:

 * d1 must be defined, presumably to a 1 following the
   patterns of other decimal numbers.

 * variable xx must be renamed so it doesn't clash with
   the xx instruction mnemonic used by the perl cross assembler.

build/proto

@@ -50,6 +50,7 @@ dd           drwr- -1 4
         nm       frwr- -1 bin/nm
         od       frwr- -1 bin/od
         p        frwr- -1 bin/p
+        psych    frwr- -1 bin/psych
         rm       frwr- -1 bin/rm
         rn       frwr- -1 bin/rn
         roff     frwr- -1 bin/roff