Replace enums with simple defs, replace kb routine with asm

calypsi uses "int" as the type for enums, also replace the basic
keyboard routine for key reading with an assembly written one

src/input.h

@@ -3,16 +3,14 @@
 
 #include <stdint.h>
 
-typedef enum {
-	K_NONE = 0,
-	K_UP,
-	K_DOWN,
-	K_LEFT,
-	K_RIGHT,
-	K_CTRL_R,
-} key;
+#define K_NONE	0
+#define	K_UP	1
+#define	K_DOWN	2
+#define	K_LEFT	3
+#define K_RIGHT	4
+#define	K_CTRL_R	5
 
-key read_kb(void);
+uint8_t read_kb(void);
 
 uint8_t read_any_key(void);