add fac example

testfiles/fac.f

@@ -0,0 +1,21 @@
+: fac ( num -- out )  
+  dup 1 > if dup 1- recurse * then ;
+
+: 0bye ( num -- ) 
+  0= if bye then ;
+
+: xdrop ( count -- )
+  0 do drop loop ;
+
+: >single ( c-addr u1 -- u2 )
+  0 0 2swap >number 3 xdrop ;
+
+30 chars buffer: buf
+
+." Number: " 
+buf 30 accept dup 0bye
+buf swap >single
+
+." Factorial of " dup . ." is "
+
+fac . cr