Make key-bindings for INPUT more shell like: CursorUp/CursorDown

cycles through the command history.  Use Ctrl-p/-n to move cursor to
the previous/next line in the input.

scheme/input-buffer.scm

@@ -91,19 +91,19 @@
 		  (set! pos-col (- pos-col 1))))
 	    values))
 
-       ;;Nav
-       ((= ch key-up)
+       ;; move cursor to previous line Ctrl-p, keycode 16
+       ((= ch 16)
  	(if (< pos-fin-ln 2)
  	    values
  	    (let ((length-prev-line
  		   (string-length
  		    (list-ref text (- pos-line 2)))))
-	      (begin
 	      (set! can-write #f)
 	      (set! pos-line (- pos-line 1))
-		(set! pos-col (+ length-prev-line 2))))))
+	      (set! pos-col (+ length-prev-line 2)))))
 
-       ((= ch key-down)
+       ;; move cursor to next line Ctrl-n, keycode 141
+        ((= ch 141)
  	(let ((last-pos (length text)))
  	  (if (>= pos-line last-pos)
  	      values
@@ -152,8 +152,8 @@
 		(set! text (append text-front '("")))
 		(set! pos-col 2)))))
 
-       ;;Ctrl+f -> History-forward
-       ((= ch 6)
+       ;; forward in command history -- CursorDown
+       ((= ch key-down)
 	(if can-write
 	    (begin
 	      (if (< history-pos (- (length text) 1))
@@ -167,8 +167,8 @@
 				  (list-ref text (- (length text) 1)))))
 		    (set! pos-col (+ line-length 2))))))
 
-       ;;Ctrl+b -> History-back
-       ((= ch 2)
+       ;; back in command history -- CursorUp
+       ((= ch key-up)
 	(if can-write
 	    (begin
 	      (if (> history-pos 0)