Add KIM-1 functions to write to the 7-segment LED display and get

keypresses from the keypad.
Includes sample program illustrating how to use them.
Tested on real KIM-1 hardware.

libsrc/kim1/getkey.s

@@ -0,0 +1,18 @@
+;
+; int __fastcall__ getkey();
+;
+
+.include        "kim1.inc"
+
+.import         popa
+
+.export         _getkey
+
+.proc           _getkey
+
+        jsr     KEYIN           ; Open up keyboard channel
+        jsr     GETKEY          ; Get key code
+        ldx     #0              ; MSB of return value is zero
+        rts
+
+.endproc