Fix 1994/horton/Makefile and README.md

The alt code was being compiled with 'all' rather than 'alt'.

The README.md file also has had format updates including referring to
the alt code as well as the gtface.c.

This should complete 1994/horton.

1994/horton/Makefile

@@ -114,10 +114,10 @@ PROG= ${ENTRY}
 #
 OBJ= ${PROG}.o
 DATA= gtface.data
-TARGET= ${PROG} gtface ${PROG}.alt
+TARGET= ${PROG} gtface
 #
-ALT_OBJ= ${PROG}.alt.o
-ALT_TARGET= ${PROG}.alt
+ALT_OBJ= ${PROG}.alt.o gtface.o
+ALT_TARGET= ${PROG}.alt gtface
 
 
 #################